If youve finished it with a char once and you start a new game you can choose to "import" a ME2 char if you do that you get the following:
- Keep all HEAVY weapons.
- Get extra recources and credits at the start.
- Get 25% more exp
and if you import a ME 1 char you get:
- 1000 exp (start at Lvl 2).
- Extra credits if you ME 1 char was rich.
- Different encounters than normal (meeting extra people!)
Your starting level based on your ME1 save is based on what you achieved in ME1. If you were a complete badass in ME1 ie both DLC lvl 60 etc you start at lvl 5.