Just returned a crock of sh*t 54 plate new shape astraÂÂÂ

'an bought a 51 plate 5 dr 1.6S golf instead. Nice (dont laugh) condition in met black.
Gonna pimp it up (as you do) but would like some advise first please....
1. Lowering springs - are -35mm springs ok for 17" & 18". Would the shocks need uprating for 18"
2. Much of a job fitting them???
3. Do 18" alloys punish the wheel bearings on Mk4's
4. Mk4 PCD = 5 x 100 right?, unsure of the offset.
Any help would be greatly appreciatedÂÂÂ

Cheers,
Stu