Mass Effect 2: Create a new character?

Starting a new character on any version of ME2 will not effect your previous character, the game's "careers" have their own section for each of their saves. I imagine ME3 will import in much the same way ME2, in that you select a previously completed profile from a list of saves from the previous game.

i play mass effect 2 4 times and mass effect 1 3 times

mass effect 2 saves are in careers you see it when you load the game the original one the first walkthrough will be separated from the second one in other words when you get mass effect 3 and want to import a mass effect 2 save to 3 it will ask you what career you want to import meaning the first or second walkthrough

Yes you can save your prior characters. And each character will affect the Mass Effect 3 gameplay depending on which character you choose. I have several saves from Mass Effect 1 and they each had different outcomes in ME2.