Its always a great IDEA.....but when put into practice and slap a little reality in there...there's much better money that could be spent.
However, 2.5T + Stage 3 on a Golf R platform would not only be NUTS, but would require some serious stability mods.
if you want that on a golf R platform, just get the TT-RS. it is basically the same platform with all those extra stability mods already thrown in. plus better weight distribution with the use of aluminum.
whatever you want it to run. it's a build yourself, but you'll need a RWD donor. figure $1000 for a wrecked donor car, $500 for a decent welder... i think another $1000 for metal other bits and pieces. probably $2500 is my guesstimate for a decent build.