First of all take a long hard look at your bank account !!! because it will never be in the black again , worse to upkeep than a victorian terraced house with damp !!!!!
Seriously though, MK5s are tanks. There is nothing on them that I would consider a bank buster unless the car is very obviously a beater on first glance.
Manuals - strong as an Ox. Needs a clutch if you push the torque up with a remap. Standard.
DSG - the physical gears and clutch packs = bomb proof. If you need a mechatronics unit because of slack previous owner maintenance, well, stump up a grand and you're golden again. For a performance German car, a grand is peanuts imo.
The electronics - apart from the alarm module - are solid as Edwardian mansions. Any issues there will be down to previous owner stereo and accessory installs. Badly coded can gateway upragdes and what not. Door and boot modules can go, but they've since been updated. The newest boot module for example, latches/unlatches twice as fast as the original, so if it goes - yay, time to upgrade
The chassis - epic. What the MK5 is all about. Apart from the William SHATner standard console bushes and standard springs that like to bust a pig tails, it's all very tough. No worries there.
Rusty wings - no biggy. Get them replaced by VW if they're starting to rot. If you're outside the 12 year warranty period, the wings are cheap from VW.
The only 'quality' issue I have noticed on the MK5 is the interior. If previous hack job bodgers have been in there and pulled it apart, that's where the rattles come from, otherwise it's solid.
Buy on condition. Mileage is irrelevant. I've seen 50K MK5s that are shabbier than 150K examples. It's all down to the previous owners.
One final piece of advice - Walk away from any car that is sitting on Chinese ditch finders. It speaks volumes through a megaphone on max volume about the car's standard of upkeep. VW fitted either Pilot Sports or Conti Sports to these cars as standard - so if it's riding on 'EggsNow ChunkyFun IceySkateboard' tyres, swerve it.