I'm a nervous mechanic when I'm opening a new part of a machine. I read about it, and watch YouTube videos first, but sometimes you just need to take it apart and see.
Airbox rubber - leave the airbox in place, no need to remove it, and remove both rubbers and the carb at the same time. Refitting can be tricky, but I think I used a bit of washing-up liquid as lube and it all fitted together easily enough. I did this a couple of years ago, and it doesn't stand out in my mind as one of those evil jobs, so it must have been easy enough.
I cleaned my carb using a small ultrasonic cleaner that I got from Lidl for £20. With the carb off the bike, rotate it slowly and try to drain all the petrol out of it, sometimes you need to roll it round several times to get petrol out of all the corners. Dismantle the carb slowly, on a tray in case you drop something, be aware that there may be a bit of petrol still inside, photograph each step, put all the bits in a take-away box. Nothing's going to leap out and bite you. Clean all the parts, and don't stick metal things into any of the brass jets. All the jets are on different threads, so you can't put them back in the wrong place. I bought a new carb gasket set from eBay - search for Dellorto 52514 - only £15. The carb is a Dellorto PHF 34, the gasket set is the 52514.
Replacing the timing belt is easy too. Make sure it's an automotive application belt - get it from Sportax, Force etc. One tip I read was to cut the original belt in half along its length, leaving a half-thickness belt on the pulleys, then slip the new belt onto the pulleys, then cut off the remaining half of the original belt and push the new one all the way on. That way the crank and cam shafts are never free of each other. I think I just marked both pulleys and the engine casing with pencil marks, took the belt off completely, and made sure all the marks stayed lined up. Like the carb, the first time was tricky, and after that it's easy.
The indicators for my SS were actually Guzzi items, and I got replacements from Gutzibits. I think a lot of the switchgear is Italian, so your indicators might be too.