You car drill them, but the hole needs to be so large to not trigger the EML as to render the blanking plate useless. It would make more sense to blank it normally and clear the code every so often with a cheap code reader.

Either that or just clean it out every few thousand miles.

All the main points have been covered - but I would say that £2k is top whack for a 2005 115.

They're great cars when they work well, just pray you don't suffer from injector issues as it can get very expensive, very quickly. You don't mention the mileage - but if it's over 80K then I'd want receipts for replacement injectors. If not, they could pop at any time (or be fine for thousands of miles, it does seem a bit random)

I'd be surprised if you saw 50mpg - the norm seems to be low to mid 40s with mixed driving, but it may be a good 'un and you may get more.