Go to a good camera store and check out Sony cameras. I think you will be pleasantly surprised. The problem will be how will you attach the lens if the Tamron does have a Sony mount. Try the A37, A57, A65 or A77 with your lens and see if they will be compatible.
Trying to hand hold for long exposures is not very feasible. The in camera IS works best when shooting at a fairly fast shutter speed compared to a long exposure. Turn off the IS when shooting long exposures from a tripod as you don't need it. As Snowbear stated it usually degrades your image. But try is and see what happens.

Since the Pentax has IS build in why will it not work for you for hand held, and turn it off as recommend for tripod use since you don't need it?

Only if it is out of place and you don't eat it.

I believe that is a small wasp. It has wings and no elbowed antennae. It must have been moving to not be in focus.