It shouldn’t be a hassle for wheels with a centre bore that’s greater than 57.1 as spigot rings of the appropriate size are fitted inside the centre bore of the wheel to reduce it to 57.1. Aftermarket alloy manufacturers tend to make many of their wheels with a relatively large centre bore so the wheels will fit as wide a range of different vehicles as possible (with the appropriate sized spigot rings fitted to the wheels); that way they can maximise their sales volumes!
Wheels with a centre bore of less than 57.1 won’t fit. Additionally, all wheels for the Polo will need to have a PCD (pitch circle diameter) of 5x100, otherwise the bolt holes in the wheels won’t line up with the corresponding bolt holes in the car’s hub assemblies.
It’s really important that the wheel’s centre bore fits snug and flush on the car’s hub as it’s this snug fit that takes the weight of the car. If wheels with a larger (than 57.1) centre bore are fitted without spigot rings, then the wheel bolts will be taking the entire weight of the car, so they’ll be under considerable strain and at risk of failing and IMO that’s incredibly dangerous and unsafe.
Ensuring the fitmemt of aftermarket wheels is correct for specific makes and model of car is the reason why online retailers require you to input details of your car. That way, they’ll only show you wheels that will fit your car. Some of those wheels will have a centre bore larger than 57.1 and some will require wheel bolts with a tapered or flat seat rather than use the existing VW radius seat wheel bolts. If that happens to be the case, then the retailer will supply a fixing kit comprising bolts and / or spigot rings to ensure correct and safe fitment of the wheels on the car. All wheels they show you should have combinations of wheel width and offset that shouldn’t give you any rubbing issues. However, on that point I would personally always stick as close as possible to the width and offset of VW’s factory wheels. Bear in mind that if you need new wheel bolts, the fixing kit the retailer provides is unlikely to include locking wheel bolts, so you’d need to buy new locking wheel bolts with the correct bolt seat (tapered or flat) for the wheels. It would also be advisable to keep the bolts off one of your existing Brescia alloys in your car in case you ever need to fit your space saver spare (the space saver uses the existing radius seat wheel bolts).
Lastly, fitting different wheels is a modification, so you’d need to let your insurer know. My insurer didn’t change my premium when I advised them I’d be fitting different wheels - they just wanted to know the value of the wheels.