If you Google for "Omeg 4mm" you should get enough hits to point you in the right direction for replacement pots.
My view on capacitors - replace electrolytics wherever they are, PSU or not. There aren't many in Simmons kit other than the PSU so they're worth replacing. And if you're working on an SDX power supply, replace all the type X / mains capacitors (or be prepared for them to let out a huge amount of horrible smelling smoke one day).
Schematics - I agree with the previous post, some of them are good, some awful - even the simplest early product schematics have lots of errors, but they're a starting point. There is a readable SDS7 schematic out there if you look hard enough... For the products where schematics are just not available (which fortunately appears to be the minority), spend the time making your own and you'll really find out how it works !