As mactran says, extended lighting adds some nice touches that should be standard on a car this price. Not many have comfort access (keyless entry and start), you'll probably see quite a few that have 'comfort pack' - this isn't the same, it's extended lighting, wind deflector, extended storage (little compartment to the right of the steering wheel, compartment in the rear bulkhead - again, should be standard...).
The standard 6 speaker system is OK with the roof up - you can't hear it with the roof down. Not sure about 11 speakers, but 14 are good - the only addition is a midrange in the centre of the dash and a tweeter and a midrange in the rear bulkhead - and a bigger amp, so I'd think an 11 speaker system wouldn't be too bad.
Heated seats are pretty common, I think they were standard on the 30i's, my 23i didn't have them. Heated steering wheels are pretty rare. My 35i has both, I've only ever turned them on to see if they work...
Sports seats are good, manual ones have lots of levers in different places whereas the electric ones are easy to adjust - at the expense of extra weight and complexity.
As for M-Sport vs SE, I can't really comment, I have only driven the M-Sport versions. I have read that the SE suspension is more comfortable, I don't find the M-Sport unpleasant.
Hope your search is successful, not the most practical car in the world, but a lot of fun
Cheers,
Dave