I think you'll be needing a bigger intercooler - it's needed for a Polo GTI upping it's stock power by 35%, you're going way higher than that.
There's no way this all can be cost effective pushing a 1.0 engine to 170ps with (at a rough minimum guess) £4k hardware replacement costs (turbo, maybe injectors, brakes, fuel pump exhaust system, remap, intercooler , then being held to ransom by your insurance company.
All this is better than buying a GTI+ with everything suitable for its output, ACC standard fit to help with insurance premiums, despite the higher output, and a fully functioning warranty.
You'll get a fraction of that money back if you return to stock to sell it, or you'll be left with a car no-one will touch with a barge pole. The GTI+ is far better equipped as standard, with a sporty interior you'll probably want to replicate at even more expense, and residuals are noticeably better. The GTI+ will cost more than your car, but probably less than your car and all its mods, will be worth more when you sell it.
If you go to 170ps you'll need to go to RON99 all the time because you won't be able to inject enough RON95 to develop170ps without it pinking.
Seems like cost is way outweighing the benefit.