To answer the latest batch:
1. Yes, just hit Delete or backspace, and it will bring up a confirmation dialog. Only a very few structures cannot be deleted (your home command station, and a few of the specialized capturables).
2. You are correct on what you have to do in order to take that ARS. Because of the ARS, it's a highly valuable system for capture, even if it is otherwise worthless. The need to kill and then capture the planet is the cost of capturing the ARS (you may notice it doesn't come with any AI Progress or any other costs of its own).
3. If you destroy a command station and the warp gate on a planet, then you've not really bypassed that planet, you've just cleared it out but decided not to take it. For warp gates, you don't really need to clear those unless they are on a planet that is adjacent to one of your planets, and you wish not to have waves against your planet from that particular AI planet. Here is some more info on how AI reinforcements work in general, if you have not seen this:
http://arcengames.com/mediawiki/index.php?title=AI_War_-_AI_ReinforcementsGenerally speaking, if you are going to "bypass" a planet, you'd just sneak ships through and not really mess with it all. If you want to "neuter" a planet (in the community parlance), you'd might kill the guard posts and (probably) special forces guard post, and very possibly the warp gate, but you'd leave the command station intact. Thus limiting the size the planet can grow to, but also avoiding a large bump in AI Progress. Or, if you want to create a neutral buffer between your planets and enemy planets, you can just wipe out the AI on the planet but not take it for yourself. That comes at more AI Progress cost, so isn't done as much, but can very occasionally be quite useful.