Batman: Arkham City

So I'm at the end of the game (playing as catwoman headed into the museum to get her stuff back) and I was wondering what happens when its finished. Is there any opportunity to play as batman through arkham city, doing the riddler stuff i skipped and finishing the side quests i did not finish (the identity thief and deadshot ones) or am i going to have to finish them in new game plus?

thanks. also, what is the last upgrade you can get? on the gadget tab under waynetech upgrades there is a locked box, i have every gadget that i know of though
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i7 920 D0 | P6T6 WS Revolution | 2xGTX285 2GB | 12GB Corsair Vengeance DDR3-1600 | 2x600GB Raptor/ 2x1TB RE3 WD | Corsair HX1000w | Silverstone RV01

You are probably missing the last Mr. Freeze item found in the Steel Mill. It is a side quest and the game never tells you about it otherwise.

And yes, you can freeroam after you finish that Catwoman segment.
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GET AGAINST THE TREE!!!
~ The Sage of Shadow ~

will i be able to play as catwoman again or will i not be able to go back for any of her trophies?

and thanks for the response
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i7 920 D0 | P6T6 WS Revolution | 2xGTX285 2GB | 12GB Corsair Vengeance DDR3-1600 | 2x600GB Raptor/ 2x1TB RE3 WD | Corsair HX1000w | Silverstone RV01

There are 3 locations in the city where you can switch between Batman and Catwoman. You can't, won't, and don't miss out on anything important.
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GET AGAINST THE TREE!!!
~ The Sage of Shadow ~

thanks very much! :D
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i7 920 D0 | P6T6 WS Revolution | 2xGTX285 2GB | 12GB Corsair Vengeance DDR3-1600 | 2x600GB Raptor/ 2x1TB RE3 WD | Corsair HX1000w | Silverstone RV01