Wrt the outsourcing part: I have had my fair share of "outsourcing" (Indonesia, India) and I would say beware! It always sounds too good to be true and in my experience it often is so. "CMM level five, highly educated/skilled professionals, a fraction of the tariff you would normally pay etc. etc."

What they forget to mention is that the communication problems grow EXPONENTIALLY. Typically you end up with (extra) people in between taking care of this (you don’t want this job I assure you!). In some cultures yes can mean no too ;-)

You state that the app contains “few messy, undocumented, tangled bits of code and design”. You will have to sort this out first. Everything depends on being able to communicate clearly/unambiguously what you want from them. Often the design is frozen and they built it as-is with flexibility zero.

PS If you go ahead with it make sure to communicate your standards/guidelines and put a process in place to enforce this!