well, considering the kind of driving you're expecting to do, the DPF would give you trouble and the 3.2 would create its own black hole in your bank account..
Having said this, the DPF can be removed at a relatively good price and apparently it's the best thing for diesels, both for the better performance and for the slightly improved MPG, whereas there is little or no work you can do to improve the 3.2 mpg (not that I know of anyway).
In terms of maintenance, a petrol car is always a tad more needy than a diesel one, but there are other things to take into account for diesels, let me run you through some:
1) DPF: fortunately it can be removed and this seems to be the cure of all evils. The removal can be drastic or "cosmetically smart" (basically your DPF basket is emptied of its mesh). Considering all the turmoil regarding new possible regulations on MOT and DPF presence, I would recommend having it substituted with a straight pipe and keep the DPF stored.
2) DMF/Clutch: this is quite a beastie of a job, my warranty partly covered for it, but ARUK was a total biatch about it. Make sure that the DMF is in good nick (you can hear the rattle on idle if it's gone) and/or whether it's been changed.
4) injectors: had mine changed to the newer version.
5) EGR: same as above.
faults that seem to be common to all Breras are:
3) Steering servo liquid: this seems another major issue (not sure if common to ALL Breras), I had mine changed to the right liquid and a new reservoir tank was installed
4) front tires uneven wear: there's not much that can be done there me thinks, just monitor your tire pressure constantly and swap fronts with rears more often.
5) various big and small electrical/electronics snags
I'm sure I've missed a lot , but others can help