If you have your clutch lever pulled in with the engine in gear, and you can't start your engine, and your side stand switch is bypassed, then it sounds like your clutch switch is faulty.
Here's a brief diagram of the starter circuit.
As for the sputtering and quitting, it could be loose battery or ground connections, tilt sensor, etc.
I'd also check the main harness near the rear fuel tank pivot for evidence of pinching or bruising.
That harness lies very close to the fuel tank seam edge and is very easy to pinch the wiring if not careful.
Here's a brief overview of the ignition circuit.
If you don't already have a service manual, you can download it from here (suggest your get both N. America and UK manuals as the UK manuals has better quality scans):
I will say that electrical problems on these bikes is fairly frequent for several reasons.
1) The bikes are getting older and components are starting to wear/fail due to age.
2) Weather related corrosion on electrical contacts (dielectric tuneup grease is a wonder).
3) Previous owner stupidity. Probably THE number one cause of electrical gremlins.
4) Damage due to bike being laid down or wrecked.
5) Wiring harness not routed sufficiently with fuel tank lowered onto main wiring harness, causing crimped/bruised/broken wiring.
Personally speaking, cause number 3 was the reason why I had to replace all my wiring harnesses.
They were beyond salvation.