I do a bit of instrument repair, thoughts as follows:-
Screwdrivers - PB Swiss are my fav's, certainly for Metric, Pozi and Phillips, but like anything else you need drivers that are a good fit, so working on a lot of older British stuff I also have an old British made set in imperial sizes. You can never have too many drivers, so gather up old ones to grind down or consider one of the instrument sized bit drivers that take the small bits. Facom is about the nicest of these!
Pliers - I have a mix of Older British, German, Swiss and Swedish. You have to keep up to date with the quality of all these things. A lot of times you see Lindstrom being recommended, which was a good call 15 years ago, but they're nowhere the quality they used to be - box joints have given way to cheaper screwed lap joints, fit and finish are poorer, and they're not even made in Sweden any more! I'd agree with the reccomendation for Schmitz. I have a few of these and they are superb NOW, as well as being good value!
There are some patterns of regular pliers that are invaluable too. As well as Combination and Snipe Nose in small sizes I use things like Relay Pliers and Needle Nose a lot!
Other tools - I find that watchmakers tools are generally too small for instrument work, you need something a little stronger. Tweezers - I've acquired surplus medical ones over the years which work well! Add a good 1/4 drive socket set, sets of small hex and torx keys from PB, and a pick and probe set while you are shopping!
I also have an old British made gadget called a 'Multi Mini' which is basically 2 miniature vices on a versatile stand. This thing is invaluable when working in small stuff but I havn't seen one for sale in ages!
