You honestly are getting ahead of yourself. you need to do a lot of reading to prepare yourself. the e-manage will work but not too many peopel have used it that far and can guide you through it. I wont tell you to go either way because you need to choose the best way for your capabilities.

20psi will be difficult on pump gas, do you realize that? you will also need some form of ignition control like a crane ignition box for example.

what do you have to monitor air/fuel mixture?
Do you have an EGT?
Do you know what to look for when listening for knock?
Have you searched the internet for fuel injector calculators?
Do you understand the difference of a 1:1 regulator versus a 12:1 rising rate regulator?

I am not being disrespectful to you at all but these are questions you need to know and consider extremely basic when tuning. If any of these seem foggy or unclear to you, then you need to spend more time learning, asking questions, and reading so you dont waste money in the long run by breakign things. If you screw up at high boost (15+) you are not replacing small things like head gaskets, you are rebuilding or replacing your motor. That would not be fun if you werent prepared for it.

My personal thoughts are to get rid of the e-manage and go with an 8 injector setup or portfueler (from Hahn Racecraft) if you arent comfortable fabricating an 8 injector setup yourself. Hahn will also give you base maps to start with and that will make things easier for you depending on your level of knowledge.

Terry