Nuttish

The merit of illustrator or inkscape is that they make flat images as with actual paper patterns and leave everything scalable and capable of being edited as far as your imagination goes and the software supports. Yes I know CAD software can create flat vector images but it is intended for other uses and I think adds unnecessary layers of abstraction and conceptual complexity. It also lacks many of the powerful tools or workflow shortcuts that illustrator has. There is also garment patternmaking software, but its great merit is being able to grade garment patterns, which is unnecessary. You can draw vector lines in Photoshop, but it is intended for raster editing and is both extremely weak on the vector tools illustrator has and is loaded with raster tools that are useless for patternmaking. I think it's a lot easier to work with leather patterns in vector lines than using traditional drafting.

I made a friend some bike grips out of chrome tanned and learned that it stretches too much to be useful. I ended up paring and rolling the stitched edges over a piece of pared veg tan.

I would experiment with white saddle soap and a brass suede brush. Neatsfoot will dramatically darken the suede and perhaps even absorb unevenly. Washing our oiling may cause the suede to separate from its backing if any. But experiment.

I would pick up the Osborn belt punch set for $45 before you start buying better punches like Weaver's store brand. That way you'll get 6 punches in the most common sizes and be able to get a feel for what's appropriate for your applications and usually have the correct tool at hand. Also get a combination water stone, make a strop, and learn the basics of sharpening — only the best tools will come sharp enough to use. You will be delighted with the results. Round punches are easy enough to get an acceptable edge on. Use a piece of UHDPE or poundo board to preserve your edges.

I don't see what the disagreement is. Calling something vegetable tanned aniline dyed leather says nothing about its temper, grain, intended use, etc. Just have a look at Horween's full tannage list. It's got heavily retanned Dublin, less greasy Essex and Derby all of which have remarkably different tempers than equine Vermont. These all come in a variety of colors that aren't achievable with natural dyes, meaning they're likely aniline dyed and perhaps even mordanted with chromium salts to achieve faster and more vibrant colors. One point to make is that you will be limiting sources if you confine yourself to searching solely for chrome-free leather when there are many leathers that aren't chrome tanned that won't necessarily be represented as such. US tanneries will most certainly be willing to tell you which of their leathers are chrome tanned. Importers probably not so much. If you are looking not to support processes that discharge chromium into the environment, that's another deal.

Fine Leather Working overcharges for Sajou thread. It's available elsewhere for nearly 10% less with cheaper shipping.

It's fine with longer legs and a padded seat.

W&C English bridle is quite firm, but it must be repasted and finished if split or it becomes stretchy like anything else. The backs are a substantial reason the temper is so rigid. The vegetable tanned tooling and skirting also needs to be pasted. W&C's split samples are slow because they're not in stock like the rest of their swatches. They get made for you. It takes a couple of weeks.

Yes, hemp is a traditional material. Why would hemp set anything off at an airport? It's not reefer. It's fiber from the stalk of the plant and contains exactly 0 parts THC. Cotton is an alternative. Round urethane weldable belting from McMaster-Carr is an alternative.

https://www.ridgid.com/us/en/oscillating-edge-belt-spindle-sander. It's a nice machine, particularly because you can't get spindles in fine grits, but you can get very high quality 4x24 belts up to 600 from Klingspor. Many Horween leathers are much harder to work with than people give them credit for. It's hard to answer until you get more specific about what tannages you intend to use.

I think you need to do some research on your own. Vegetable tanned aniline dyed leather is a uselessly broad description.

The Tandy machined brass pen sized rollers are nice. The Tandy table top rollers are garbage. Things like this work fine and come in a variety of sizes. http://www.dickblick.com/products/molotow-empty-markers-and-replacement-nibs/

You can tie the ends together with a surgeon's knot inside the fold.

You might find Maker's Row and the various fashion startup blogs and books helpful. You're asking questions that require discussion more than an answer.1

The piece you're showing is the standard Chinese flat brass ring you can find on Alibaba, eBay, or Etsy. Uniformly not-so-great quality, although they do polish up nicely on the buffer for something I'm not certain I believe is actually brass. I've spent hours looking for reasonably priced flat brass split rings. If you find any, please pass the info along.

Horween doesn't make anything remotely close to a bridle leather like Wickett & Craig's. Their stiffest temper is probably a latigo, but it's still not comparable. Wickett & Craig may send you splits to show temper if you ask nicely. It will take a while and be low priority since they have to make them in the splitting department. Why have you chosen bridle leather? The backs are pasted smooth, so it's not going to have the same comfortable hand as a raw back like on the Orvis piece you attached.

Rigid polystyrene plastic sheets (.020") are ok for working templates.

I don't think there's a trick for perfectly centering it other than measuring the piece and accounting for the diameter of the roll. The top piece of yours looks like it has wide channel skives under the turn. That could give a clear demarcation for where to start folding the piece on each side and makes it easy to finger press and glue a straight line. Otherwise, it looks like it's glued bottom up, folded/glued, and topstitched. I'd fold last so that you can see exactly where the piece will end up on the top and align masking tape so you can get a clean glue-up.

It's not worth the time and frustration in my opinion. Barry King's awls are perfect out of the box and in sizes perfectly appropriate for your needs.

It's difficult or impossible to burnish edges with soft temper and open grain like that for at least two reasons. First, the grain will never compress enough to allow it to be sanded smooth. Second, the stretch will cause any burnishing you do achieve to open back up, causing it lose its uniform look by turning white in spots where the finish has broken up. I'd use a flexible edge paint like the Italian stuff Campbell Randall sells. It's thin, flows nicely, is mixable, and is easy to apply by hand even on thin edges with one of those Tandy machined brass edge paint rollers.

If you're looking for alternatives, I just have W&C send me my splits and use those as bag bottom reinforcements. Bridle splits in ~6oz still have a nice temper because of the gum pasted backs.

It might be sew in interfacing, which is a perfectly reasonable material to use even if it's not.

Something Tandy makes that is surprisingly good. http://www.tandyleather.com/en-usd/home/3437-00.aspx This makes it easy to apply anything liquid to edges.

+1 thoughtcrimes on difficulty and practice. Dilute dye solutions make uneven penetration quite easy to see, and the problem gets worse as you make additional applications. I use a highly dilute natural vat dye on unfinished tooling leather. I wet it out just like fabric. I find that very lightly washing the leather with dilute oxalic acid and gently washing the acid solution off with a damp cloth is sufficient to wet the leather out so that it will uniformly absorb my water-based dye solution. If you're using diluted spirit dye, you can let the leather dry from its oxalic acid wash and then wet it out by lightly spritzing it with rubbing alcohol.

Guterman upholstery thread comes in that one size, so it's not going to be suitable. If you're looking for nylon or poly, DrmCa's suggestion is good. If you want linen, try Crawford's Irish linen. It comes in a great variety of colors and plies that will come close to what you need. I get it from Royalwood in the US. I have no idea about Indonesian sources. If you're making watch straps, .6mm is an enormous thread.