Is it neccessary to restrict 650 dragstar to 25kw

2.6 litres

The side stand switch can work in cojunction with a clutch switch.
It still sounds like a side stand problem, check the wires and plug, use a multi meter to check the switch. If you didnt check it that way.
The switch may work but the stand is not pushing the contact far enough

Does the neutral light work correctly?

Assuming it is not clutch drag with the bike jumping and stalling when put in gear

First I would change all the spark plugs, and if that didn't make a difference then it sounds like the coil(s) are warming up and breaking down........when it starts to skip take a good pair of pliers with good rubber on them and pull each spark plug wire, when you get to the one that the running doesn't change then I would replace that particular coil

u really need a pro to guide ya here-bad jet settings can fry your engine--do some reading sec 629 library or purchase expert manuals like clymer

38 PSI front and rear is a good base setting

About 140$ for the fron disk...
Part n° 5BN-2582U-00-00

your tire manufacurer print on the sidewall the required pressure for your application. you should follow this restriction as required for your tire rating and application

Go to a local FinishMaster store and they will use a color eye to find u a color