Seems your early strategy works - I'd keep it that way (I'm a nit though ).
In mid/late stages (bb 200+) you need to start stealing (as you mentioned).
There's a nice article by KC about stealing that might help you: KC ADVANCED BLIND STEALING STRATEGY
There are many threads dealing with deepstack tourney play in the strategy section, too: StrategyArticles (http://www.cardschat.com/poker-strategy.php)
I know about pot -odds and being pot-comitted but for me there is no such thing in a MTT.
This is not a cash-game where you can reload instantly but it's a tourney-life decision.
Don't start limping but open your rasing range (2,5-3 BB +1 BB for every limper) a bit.
Not knowing how your range is you might consider raising small pps, high suited connectors or - against unlikely to be defended blinds - even air in late position.
If you feel your fold equity is too small because you don't have enough chips to be able to push flop,turn and river : shove and pray with hands with showdown value in order to reduce the number of callers.
M-related shove/fold theory counts in MTTs too afaik but I tend to play every tourney a bit different, sometimes waiting for my chance down to 2BBs.