You'll probably find opinions and preferences for every alternative you can think of and justified reasons why...also loads of threads on each an every alternative.
But from a relative newbie..
wheels - have had 20" with 30 and 25 profile, standard oem 19" and oem 18" on winter tyres. The 20"s looked great but in london the roads are shite especially after recent snow...The 18"s ride well but just don't look as good. So your choice looks vs ride
real world mpg - again am sure there is plenty of discussion already - i do 70 miles a day rush hr traffic and m25...never reset the tripmeter it currently reads 18.9...I've not tried to economise.
dct - is best of both worlds - jekyll and hyde - relaxed auto or ferocious neck jarring manual...but with the v8 sometimes i miss revving and inbetween gear change sound you get with manual...
as I said you will get opinions from both sides - include coupe vs conv....I would test drive especially if you're forking out new or nearly new...
2010 had latest idrive...and lci lights...so depends on budget...best advice would be test drive..
PS - Would love to be able to change my car as much as you - next m3 rumoured in 2012 with a straight 6 turbo...so this will be the last v8 in a 3....hmmm!!!
M3 Convertible 2008, Jerez Black with individual orange peel effect (factory standard), Fox Red, DCT, EDC, High gloss, carbon leather, comfort access, Logic 7, adaptive headlights, Tubi Rumore, 20" BBS CX-R, 19" OEM and 18" OEM with Winter Tyres....investments in BP/Shell