Disclaimer: What follows is a general discussion of why a certain range is profitable in a setting where you don't have great reads and will be +EV until you develop those reads. Your adjustments that you make due to your reads are what will make you money in the long run, not some hand chart. With that said, MP should still play fairly straightforward.
Middle Position (MP)
This position should play pretty much like UTG with two small differences:
1. Sometimes a player enters the pot ahead of you.
2. You are 10% less likely to be OOP postflop.
Default MP raising range: 22+, AT+, JTs+, KJ+ (13.7% of hands)
Two additions that you might notice are JTs and QJs. Those play well enough postflop to open at this point.
Limpers
This is the first position where you start dealing with limpers. Assuming that the limper has a reasonable stack (65BB's+) you can isolate them with your whole open range. No need to pot it - just make it 4x with whatever you would have opened - even 22 - and go from there. Treat them almost like if they folded.
If a limper is a short stack, just open whatever you feel comfortable playing all-in preflop vs. him.
Facing an UTG open
By default, you can 3-bet JJ+, AK for value. If you get shoved on, you should fold the jacks. This doesn't mean that you shouldn't have 3-bet them at this level - tons of people will call you with worse, but when you get 4-bet, you will often look at QQ+, AK. As you develop reads and realize that someone's 4-betting range from UTG is KK+ and they either 4-bet or fold, you can start flatting QQ and AK.
Also, by default, you should call 22 - TT, AQ, AJs, and KQs. Those should be pretty easy to play postflop.
What about suited connectors?
Meh ... how often do you win a big 4-way pot being OOP with 78s? You remember the times where you've flopped a straight and forget all the times you've bled money. Often you will flop a weak flush draw or pair + draw. Now - HU, those do really well in position, but multi-way OOP not so well.
Facing a 3-bet
Treat this just like if you opened from UTG. As I mentioned - they play almost identically.
So that's it. The really interesting stuff starts happening at the CO.