How does the replay system work?

I've searched all over the Mass Effect Wiki and can't find a page that has all the information I'm looking for. I was hoping to find something similar to the Playthrough 2 page on Borderlands Wiki but it seems no such page exists, or no such page is easily findable via the logical search terms I'm using.

I have several questions about how the replay system works in each of the Mass Effect games:

1. How many times can you replay the same character?
2. When you do replay, what parts of your character get carried over to the new playthrough?
   • Pre-service history?
   • Psychological profile?
   • Class?
   • Appearance?
   • Paragon/Renegade points?
   • Level?
   • Skills?
   • Inventory items and/or ship/weapon upgrades?
   • Cosmetic surgery?
   • In-game choices?
3. If I've played a single character multiple times, and if I can change significant decisions in each playthrough, can I choose which playthrough I want to import to the next game? If so, can I import multiple instances (from different playthroughs of previous games) of the same character into separate, new games on the sequel(s)?
4. What benefits do you get from replaying a character, that new characters don't get?

2 Answers

1 - Pretty much as many times as you want. You essentially create a new character using the last one as a template. Certain things can be changed, see part 2 of this answer.

2 - Too numerous to mention in an answer here. This is the page on the wiki you want to check out. It's also dependent ongoing from 1->2, 2->2, 2->3, 3->3, or 1->2->3.

3 - You'll get to select any save games for a character from the last or current game, so long as the character completed the game(provided she didn't die at the end of ME2). The game treats replays as a new character instances. You can tell them apart by the character level and the date on the game completion.

4 - See 2. Though generally replays in 2 get you additional credits and resources, and 3 gets you war assets.

You get the level you had on first play though, and your skills. Typically each play through you crank up the difficulty. Though they presupposed you'll do replay as same class, if you don't you only get level carry over.