20 kicks is a lot, I'd expect 2 or 3 kicks should be enough to start a motorcycle. Looking at the slingshot specs it says it's a carbureted engine, not fuel injected, I suspect what's happening is that the carburetor is dry and it's taking a few kicks to get fuel pumped into it rather than any sort of mechanical problem.
I would suggest you do the following before kicking your bike:
- Set the choke to full on for cold starts
- Quickly twist the throttle full on once or twice, this will trigger the carb's accelerator pump to squirt some fuel into the carb, so it can be drawn into the engine. This is called priming. Too many twists can flood your carburetor, so try 1 or 2 twists at first. I know some engines which need 3-4, but that's pretty rare
If you have a long lag between twisting the throttle and getting power then it could be a few things. You could have a loose throttle cable or it could be frayed, the carburetor mixture could be off, the carb's accelerator pump may not be squirting enough fuel when the throttle is applied quickly (the pump could also be sending too much fuel, flooding then engine), or the engine timing could be off. I'd suggest getting it tuned.
As for the heat, air-cooled motorcycle engines tend to get pretty hot, you can certainly burn yourself on them, so there may not be a problem at all. Slow driving will cause greater heating as there's less airflow over the engine to cool it, and if the air temperature is hot to begin with the air will cool it less. It could possibly be that your fuel-air mixture is too lean, which means there's no excess fuel to evaporate and cool the engine. Again, I would suggest a tune-up.
It doesn't sound to me like you have any real issues, priming the carburetor before kicking and getting the bike tuned will probably solve these things.