I use bleach all the time, as long as it is extremeley low strength mix of bleach water. Just make dang sure you rinse it out good with hot water, leave it in the sun as you say, and then be sure to give it plenty of dechlorinator. I haven't tried it, but you might be able to put the plants in boiling water to disinfect them. Plastics take anywhere from 400 to over 1000 degrees to melt, so it might be okay. I've always done the same thing with gravel, but it smells like you're making betta soup. Also, it washes out some of the color, so don't use it in a pot you want to keep.
Also, when you get your tank set up, smell the water for bleach. If it smells even a little bit like it, then it's no good. If you're still absolutely not sure, then put a few feeder goldfish or something in there, just make sure your water's pH and everything is the same. Myself, I've always used feeder guppies, if they die, then I know the water is no good. If they live, they get fed to my parrot cichlids.