I'd be tempted to leave it as it is with just a simple Stage 1 tune. You can use the Cossies for track work
Decent standard ones are super rare these days and there's merit in keeping it that way enjoying it for what it is
I did all the Stage 1 and 2+ shenanigans to my ED30. Stage 1 was the sweet spot, Stage 2 and above just ruined it, but then again, I did 20K miles a year in it so over the top mods are more annoying in a daily versus a weekend only toy.
But if you can't control the modding itch but want something quick and reliable, this is what I would do:
Stage 1 map.
Ohlins Road & Track coilovers.
MK7 R front brakes.
MK6 R intercooler.
Chassis bush refresh.
Eibach ARBs.
Wavetrac Diff.
And that's it. You'll have a quick car that can handle and stop. The main weaknesses of a standard MK5 are it's suspension and lack of traction out of corners. The standard brakes are OK for road use if they're in good order, but are pretty much useless on track.
In terms of power, the difference between Stage 1 and 2, or 2+ isn't night/day. The latter just adds unnecessary stress to the engine and turbo for the comparatively small gains, not to mention cost as decent 2+ parts aren't cheap. Diminishing returns and all that. Stage 1 will bag you 290-300hp, which that engine can handle all day long. 2+ will bag you 340-350 reality check bhp. Ignore the 370hp nonsense. The turbo isn't capable of that. Trust me, that additional 40-50hp isn't worth the turbo killing boost pressure, or the piston ring land breaking cylinder pressures.
Anyway, do this, do that lecturing.....it's your car at the end of the day and welcome to the fold