I've only had my MC28SP since last August so have no experience of what temperature it will hit at the lights in very warm weather, but I have used it in conditions between 15 - 20 degrees or so and it stays fairly stable at around 60 - 65 degrees. I guess this will vary massively with what's been done to your bike - mine is bog standard except MMax pipes (and a rejet I think). Maybe yours has been tinkered with lots and it is running closer to limits and is kicking out more heat.

I think the warning light comes on (to right of side stand light) if it is over heating. Probably at something like 100 - 105 degrees celsius.

As far as warming up - this was covered in a post recently so might be worth searching for it.

My opinion only - You don't want to start giving it the berries from cold as it won't like it. The temp gauge starts at 35 degrees I think, and I leave it ticking over on choke till the 35 degrees appears, then I close choke and I give it gentle blips of throttle to 3 - 5,000 rpm till it gets to 50 -60 degrees. I will still give it a few miles once moving with only partial throttle and mid-revs to give the engine time to warm through properly. But I have quite a lot of mechanical sympathy - at least till she's ready for some stick .