I haven't played fallout games nearly as much as a lot of people but I did play 3 and if I remember right had to have a save point before the last mission on the main quest to go back and do all the side quests. Is this still true in 4 or can I go and finish the main "story" then do all the unfinished side quests after?

Maybe to early to ask this but still curious.

The main quest does not end the game, you can keep going as long as you want with no level cap and no ending. Just know some quests are timed so do not take too many at once.

Although be aware that the further you advance in the main quest you might not be able to do some faction specific quests.. So don't rush through the main quest even though the game doesn't end after. Atleast this is what I've heard.