Switching from IHI to ???

Another question from the newby.....

I purchased and 88 TC motor and IHI turbo for my 1985 Mustang. After doing some research I have decided to dump the small IHI and go T3/T4 hybrid. What is confusing me is the internal and external wastegates, and oil and water cooling models VS just oil cooling models. If I want to swap out the stock 88 TC IHI for a T3/t4 hybrid do I get an internal wastgate or and external wastegate and does it matter if it's oil and water cooled or just oil cooled? I looking for a replacment turbo that will bolt right into the current setup with little to no modifications. I don't want to have to buy 50 other parts if I don't have to to get the new turbo to work. I would rather get the right parts first. Also what would be the best A/R for each side on my combo? I will be running a 88 Turbo Coupe Motor, Big VAM, LA3 ECM, front mount volvo intercooler, 5speed car. I will most likely drop in a ranger roller cam as well. I'm looking to run upwards of 20 to 30 PSI of boost.

Thanks guys.

Mike

Come on guys I know one of you turbo experts has a suggestion on a turbo size for my combo. I know I will be getting a T3/T4 hybrid but what would be a good A/R size on the turbo to acheive the boost I'm looking for and still spool quickly?

I have seen listings for T3/T4 turbos but they all have different A/R's. I won't be reving above the LA3 computer limit. And I left out the fact that I'm using a 2.3l T5 and 8.8 with 3:73 gears as well.

I pretty sure it doesn't matter if I use a water and oil or just an oil cooled turbo correct? I just plug off the water inlet and outlet right?

Mike