Thomas Alsterfalk of TME visited last month and he and I put some notes down about possible future staged kits beyond what we are currently offering. It will probably be summer before I have any prinicng or intstallation informaiton, but here are my notes on the '98 T5, which seem to echo what johann shared.
870 T5 1998 T5
ECU & Exhaust 275 HP
Downpipe 285-290 HP
Stage 3 300HP
Mitsu-18-T ( spool up will be slow with auto trans)
Wastegate 300/70 from 2000R
Stage 4 310 HP
Exhaust manifold (850R 1996 850R Euro version)
Stage 5 Intercooler from TME 315-320
No injector upgrade needed stockers are good up to approx 350 HP
Hope that helps!