WoVo

The DSC -246 is basically a Pfaff 335 clone with very similar capabilities. So if the 335 didn't fit your type of work, you should expect the same for the 246...

There were rougly 10 different hooks for the 545, depending on thread thickness etc. Your hook/machine is set up for very thin thread (likely textile garment production), so no open notch. Likely max. NM 100 thread. Good thing: You could still get parts and adjust the 545. What thread are you intending to use?

The "bar" is the lever for knee or foot lift. Pfaff 27/28 and Adler 48 are very similar, you'll find the manuals online.

Very good machines indeed. The walking feet/needle feed versions of the Adler 105/205 and Singer 45K (and it's Seiko, Ferdinand and Cowboy clones) are a bit weaker (=more joints/moving parts) than the solid frame versions but useful for slippy materials and some kind of work like saddles.

A 205-64 is not a walking feet (-370) but a needle feed sewing machine. One of the best made in the class of super heavy arm machines.

Could you supply a picture of your tension assembly and thread at the point, where the needle eye just enters the fabric?

I might have some spare screws. Based in Germany. Actually your 105 has been rebuild to a 105-6 standart to work with a roller feet, does the presser feet rod have a flat and bolt hole? I might have also some feet.