1.8t's are easy to put in, some easier than others (DBW or cable) If you have a complete doner car nearly all the bits you need can be fitted to the mk2. A custom downpipe will either need to be made or bought from QPeng. Qpeng also sell a modified engine loom & mapped ECU making the conversion plug and play. The ECU has switchable map. Depending on your 1.8 t engine. 150/180bhp,180/210bhp,225/250bhp.
Which 1.8t engine are you planning to use? I did a vr6 conversion because I found a good engine for peanuts but if going 1.8t I recommend sourcing a 225 BAM lump, my friend put a 225 lump in a mk1 and it was seriously quick! (Engine was also bought from QPeng)
G60 engine mounts can be used or buy aftermarket
G60 brake upgrade is necessary
Fuel pump & fuel lines (depending on which mk2 model you have) mk3 gti/vr6 tank&pump go straight in.
Clocks (you can use either but loom needs to match accordingly)
Budget for decent tyres!