Heat forming PVC pipe can be tricky. Sometimes it helps to put a spring inside, or sand (you can heat up sand in the oven and warm the pipe from the inside too, but more involved), so that it doesn't kink. You need to gradually bend a radius slowly, not just bend it 90 degrees or over heat the pipe.
By close off the pipe you mean heat it up and squish it so its flat on the end? I mean ya, I suppose you could do that. Could put some cement in as you do it.
You can sleeve a heated up pipe over a another pipe of the same size (like some pipes come from the store), and then glue them together again after it cools, instead of using a coupler.
Every fitting you use creates little gaps and pockets for crud to build up in. That's why I like to run the pipes with the least amount of fittings possible. It flows better too without the sharp 90's to go around. I think of it as, PVC pipe is cheap anyway, and you should replace the main sections every few years so it stays sanitary. When you use so many fittings, it cost alot more to replace when you do as well.