This is my first post. I like you joined the forum because everytime I searched it led me back here.
I was in the same position you were in. I ended up going with The Class 4. I personally spent time with David and Steve at the shop and they were very knowledgeable and helpful. It doesnt hurt that I live 15 mins from the shop so it was an easy choice for me but regardless I would do business even if I was far away. They are VERY helpful.
I was initially interested in the class 18 because I mainly do wallets, guitar straps, watch strap, pouches. Generally smaller goods. I did mention I wanted to get into bags and bigger items. This led me to the bigger machines because of potential thread limitations.
Class 3 and Class4 are the same except for the obvious difference in arm sizing. I was leaning towards the 3 but the price difference between the two is nominal so I figured might as well buy the bigger one just in case.
My only regret is not buying the prem package and going with just the standard. The extra feet, edge guide, and table would have been useful for me since this will be my only leather machine for awhile. It will need to handle a multitude of tasks.
Well thats my story. I hope it helps.