Before somebody says "Have you tried using search?" ...
Try using some punctuation and the Enter key.
Yes the factory ecu will work with a 4AGTE safely up to 12-13psi (mine has done 12.5).
I had a cusco pulley with the ZE and put down 106rwkw. I am expecting to put down at least 120rwkw with the TE on less boost.
Cost is a it depends answer - plan it properly and work out how much you can do yourself. Use search, here and google.
Research the turbo manifold designs if you can make your own. There are a lot pictures available on the web. I recommend reading through the posts on here - http://www.mr2oc.com
Having done the conversion from ZE to TE I think its a worthwhile conversion but keep an eye on the costs.