Looks doable.
7 nights Pattaya? Do you like entertainment?
If so, you might consider cutting Krabi, apart from a few bars on Ao Nang there is not much to do entertainment wise. Phi Phi is one of the world's beauties though, don't cut that. The most beautiful location and also the most remote, is Laem Tong beach.
And in case you did not know, the entertainment location on Phuket is Patong beach. Again if you like to have a lot of entertainment in Phuket make sure you get a place in Patong otherwise you are going to pay a lot for tuk tuks and taxis.
One more thing it does not make any sense to go from Phuket to Phi Phi to Krabi and then back to Phuket. You waste half a day and money traveling back to Phuket in a boring bus ride. Just stay the 7 nights in Phuket and from Krabi fly direct back to Bangkok. Remember one way tickets are just half the price of roundtrip tickets.
So when are you going so we can help you in giving you estimates of costs?