Sorry to hear of your rollercoaster day - and it's only lunch time!!
The wheels are good quality - just not AMGs. Buyers - and insurers - tend to prefer originality, but if you like them and the insurance are happy, then everyone's a winner.
With regards to warranty and where to buy from next time: private, independent, or main dealer, bear in mind that the Tier 1 warranty is the same in all but name as the Approved Used Warranty, with one difference - MOT cover is included in Tier 1.
You would be equally well protected warranty-wise with a car purchased from an independent or private seller as you would a main dealer if you get a Tier 1 warranty.
However one thing to consider is that a private seller - and many independents - might not be as flexible in the event of a non repairable problem, like you've just experienced, eg discrepency on spec or history.
The Tier 1 warranty will give you peace of mind for at least 12 months - giving you time to decide if you bought a peach or a lemon. Do shop around as some dealers may offer a free or cheaper inspection in order to get the warranty sale - even dealers which are part of the same group sometime compete on price!!
Alternatively shop around third-party warranties. Tesco Finest seems to have a fairly good reputation, it pretty comprehensive, and good value. You also have the Tesco name to use as leverage should you encounter problems in the event of a claim. They're also AMG friendly!!
Keep us posted on what you do next.