A little late (but never is too late)
For belts and idle tires take a look at Webspareparts if they have any for your deck. I have used them and they offer good quality. Unfortunately, they don't have a variety of pinch rollers but you can ask! They are in Portugal but they charge reasonable shipping fees.
For your old pinch rollers: if I understand correctly, they have a barrel shape. I have seen this shape on some old decks and I think it's not a problem as long as it doesn't cause tape skewing. Or worse, tape chewing. As said before, you can sand them a little to bring at surface some fresh rubber but if they have been rock hard or cracked, no good. As for cleaning agent, isopropyl alcohol is quite safe. Never had a problem and I use it very frequently (I'm overdoing with cleaning). To be honest, I have used stronger solvents on pinch rollers and they stand great (terebinth oil mixed with alcohol or worse, benzine). Remember that if you replace the pinch rollers (especially the take up - left) this will introduce some azimuth deviation and it will need realignment.
For your old L-R imbalance, I wouldn't touch a calibration screw until I had access to a good level/azimuth test tape. Without a test tape no one can be sure if the imbalance is at playback or at recording part of the deck (or at both). You have to be sure that your playback levels are correctly so you have it as a reference to proceed to rec adjustments (levels and bias).
As for the transport, I wouldn't touch a screw unless I was sure it's misaligned. These dual capstan bastards need a very careful adjustments in order not to chew tapes. You will need an M300 gauge and a mirror cassette. These tools are quite expensive and don't worth it if you want to fix a single deck. You can always use a homemade "mirror" cassette if you know what to do (a cheap TDK D with clear shell is a good candidate). Also, the back tension plays it's part in tape path stability. I have learned all these the hard way (and some TDK SAs eaten).
You're deck is a beauty. Don't know it sonically but it's made at the heyday of the cassette era.
Happy new year!!!