My two cents...
About the film, and the frames on it:
I like not to need to crop, and when I occasionally print in the darkroom, I print full frame.
with that in mind, be aware that:
My IIIf's have a small pusher that make sure the film is at the right height, so you won't have the sprocket entering the frame.
for some reason, my old III have a larger inter frame spacing (or is it the frames that are smaller). At any rate, on a IIIf (and maybe c) and specially with wide angles where the images gets even bigger ( "crawling" under the camera window), the frames are almost touching each other.
You may not care at all about these issues, but they are there.
in the end, with the few barnacks I had, I always needed new shutters curtains and beamsplitters.
Also, do yourself a favor, and buy an external VF. These really change the camera ergonomics.
I prefer cutting the leader than using the "B" method, simply because I don't like to have my lens rear element open too much.
You can use cassettes (FILCAs or IXMOOs).
Tons of great glass in ltm, some of it very pricey...
Good luck!