1) Don't colonize the first planet you scan. Look up the sizes.. Look up the yields... Try to keep scanning until you get large or better.
2) Don't buy terraforming or other planet improving artifacts with GP. There is no way to adequately defend a planet in this game. That is by design. All you are doing is improving the planet ultimately for someone else. There are mechanisms that can remove them from your scanner list after they've been taken too, so if you have a really attractive planet its going to be taken by the first big monster player that finds it.
3) Realize that you have 2 weeks or until you hit level 20 to not have your planets attacked. After that, fish gumbo. Enjoy them while you can.
4) Attacking each other at low levels isn't going to buy you anything. If you hack, you risk giving up planet locations (or getting some). If you raid, you risk losing valuable crew members for a handful of research points. You're not likely to get any ore from a low level player. You aren't likely to get any high level artifacts either. You're better off buying scanners and looking for planets. You are better off advancing from doing the missions than from attacking others too.. you get useful items doing the missions.
5) Realize that you can uninstall items from your decks and store them into cargo. That allows you to swap in and out scanners with other equipment.
6) It would appear that building a legion is very helpful. It gives you bonuses just for sport. You have to friend people into facebook to get them into your legion here. If you want to ally someone in game, you'll probably have to give them your email address for your facebook account. That seems like a big negative to me.
7) You can't restart the game once started. You can't change your class/character once started.
8) The developers are incredibly responsive in these forums. Ask and it will be answered.

Nice idea, there are plenty of things I wish I knew when I started. But I think some of your points are colored by personal experience or opinion and are not entirely accurate...
1) Yes, that's probably the most useful tip for a new player. Yield is more important than size though in the 1st few levels... Don't build on anything below average!
2) Hardly a tip for a new player, they're not likely to be getting their hands on terra devices. Even so, there certainly ARE ways to defend planets, via defenses, guards, cloaking.
3) You make it sound like it's a feeding frenzy as soon as people hit 20. Not so. The possibility exists, awareness is good, but it is not the norm. I have never had my planets attacked.
4) Plenty to gain from attacking, especially if that's your play style. XP potential is much higher than most missions. Personally, I agree about raids, nothing is worth risking my rank points crew. But that's my preference, others have reported big artifact wins. (You'll never gt research points from raids though, you might be mixing that up with hacking.)
5) Very true.
6) Building a legion IS helpful, for passive planet defense bonuses AND for various other reasons. Yes you DO have to invite them as a facebook friend, that's standard in 99% of all facebook games. Whether or not you publish your email is up to you.
7) You can restart your race/class at any time using GP.
8) Yep, Dan is awesome.