Mass-effect – What level will a non-imported character be at the end of the game

Firstly for an initial point of no return - as soon as you get access to the Sirta vendor in the Hospital ward buy a/the present/s, completing missions removes them quickly before you know their value.

Secondly before beginning Priority: Tuchanka you should finish off as many sidequests as you can, since completing it renders some sidequests as failed. Don't panic about having some remaining in your journal however, a few don't have their locations unlocked for retrieving quest items until later.

Thirdly Priority: Cerberus Headquarters is the point of no return for the rest of the sidequests. You can still use the onboard vendors on the normandy to purchase goods, but because of the price markup on the ship it's better to visit them directly for whatever you need before commencing this mission as well.

A newly created Shepard starts at Level 1.

Early levels go by very quickly however. For example, you'll be level 3 by the time you get off of Earth. Additionally, your opponents are scaled to your level throughout the game, so once you get past the first few levels, (where a lack of available skill points hampers your tactical options), you shouldn't have any particular problems being a low level character. It might make reaching level 60 in one play-through more than a bit problematic however.