well, the HU, not at all single din slot, not connectors needed (IIRC)
Amp - not really, get the power cable through the bonnet release gromet or drill a new whole (rca cables can make it a bit tricky to get HU back in - only in rare cases!)
Sub - same as any car if its in the boot
comps - 13cm in doors, maybe a little cutting of door cards and a little sound deadening needed for best sound, thats it (if using standard cables, if not just drill new a small whole - easier than drilling through the connector block IMO). Tweeters, can go in stock locations, may need to remove dash (not hard at all) but not great staging from there, but mounting on a pillars easy, and good staging
try it, it you ruin the a pillars its not that expensive to get new ones! if your nervous about drilling go to an ICE shop and ask them to do that bit for you, not much else to worry about!
HTH
Rorrie