Hmm if you really wanted to be technically correct there is no such thing as fully functional birth control... (So would need say a .01% chance maybe?). Although they do greatly reduce the odds.

You can edit the town to some extent.  Not the block layout but you are able to bulldoze/create homes etc.  To do this click the '...' options thing in the bottom lefthand corner then go to 'Edit Town'.  From here you can edit houses, evict families, move in families etc.  To return to playing you click the button up the top in the middle in the Edit Town mode.  Something to keep in mind if you want to move your sims to a different house is that you can use the cellphone and click move. (Only recently got the sims 3 as well).
Sims will talk about some interests though it isn't quite as extensive i guess as in the sims 3... (eg they can enthuse about books).
From what I understand you can turn off story mode (I haven't however I don't get why almost everyone except the loners appear to have partners already when you ask them if their single...).
BUt yeah there are some things i find clunky/unintuitive as well... such I would prefer to be in edit town to start with rather than create sims mode...