1)Stay with s5 13BT

2)Keep in mind.. if you port,You should/will need to go.
Bigger injectors
Better fuel pump
Fuel pressure regulator

Bigger Turbo
FMIC
BOV
Waste Gate

Thats just for add ons.
Engine/tranny/drive shaft/rear end/Engine harness/computer/fuel pump is about the basic items you need for the swap

Go J spec,and just throw the stock engine in,you have to much to worry about,and not really much mechanical knowledge to do it on your own.You have so much to swap,and its your only car and a DD.