the limits of FWD cars are being rewritten all the time.
the mk5 handles it well
DSG is a preferred option, commands resale value but expensive if it goes wrong
(so on high mileage GTI's its probably a negative not a positive resale thing)
as neg says its way better than automatic and can now have the software that controls it remapped.
you need to try both a manual and DSG mk5
you may wish to consider the ED30/Pirelli as it comes with the K04 turbo , so as std its quicker and the potential for remap gains is even better.
Nowt wrong with a remapped K03 (std GTI) anyway, can be just as good.
with good map/tyres , the mk5 handles up to 300bhp quite easily in the dry.
wet , well its more down to your ability to modulate your right foot.
I would suggest staying away from 'copy' wheels unless you can verify strength and weight.
(often they weigh a ton and will blunt the GTI's handling traits!)
Choice is wide and varied , just take your time and trawl the endless mk5 based info
good luck