Yeah, a 1.8 won't cut it; if you're going petrol then get at least a 2 litre. The 2.2 petrol isn't common but I can vouch for it being a great engine; good balance between power and economy, and certainly feels very sprightly (in the Coupe at least; no2lurch has a 2.2 SRi estate and can vouch for the engine in his car). The V6 is apparently a very nice engine but I've not had the pleasure of driving one (or even being driven in one) to comment.
Diesels are not my area of expertise, as I've never had one of them either - though I'd guess the 2.0 HDi 110 is likely to be the best of the HDi range (by which I mean there's no diesel particulate filter (FAP) to worry about like you do on the 2.2 HDi, but has more power than the HDi 90). You can remap the diesels to get more HP, higher torque, and better fuel economy. And if you're into using vegetable oil, you would need to use a Mk.1 406 with a 1.9 litre turbodiesel engine (though again, I can't give any advice on this approach).
Sorry to hear about your 406, if the car was that badly damaged, the Mini must have been going at some speed. What state was the Mini and its driver in when he'd finished "parking" it?