As I don't own a BR drive in my computer, I cannot test, but I think
1) the hardware shouldn't matter, unless you buy it off an UFO; though it appears you need to have kernel support for the filesystem in order to use it, and the latest kernels should have it. At least this is what they say at Ubuntu
. I would still expect some problems with BR discs, because even some DVDs cause trouble, even today with all the software available to get around encryptions.
2) For this I suppose either all BR drives would be able to do that (why would anybody want to make non dual layer burners, if dual layer discs have existed for so long already?) or the functionality is upgradeable as a firmware upgrade. Of course you can ask this from the store, and if they can't verify what the drive is able to do, they'll ask the importer or manufacturer.
3) See the Ubuntu page I linked to; it should be possible, though it looks tough at the moment. And like I said, expect problems, at least with some discs. I've never had trouble with DVD movies before, but a couple of days ago I met one that just didn't play no matter what..
All in all, I think it's more a matter of time than hardware to get it working. If you feel like buying a BR writer, why not, but personally I'd wait a little more for two reasons: 1) the prices are high still, but will be coming down as happens with all hardware at some point and 2) if you buy your drive now and it works as you wish at the hardware level, current software problems (namely encryption related) may hinder you for some time, and when you get over them, your drive is probably "old and slow".
Be careful with the specifications when checking out stores; if they don't mention something, you may well expect that to be really a missing feature rather than a forgotten spec. Since they aren't pocket money cadgets as of now, better ask the seller beforehand and make sure what you're buying. Good luck with your "project", I hope you'll get the data and movies working!
I'd probably consider this myself, but for the reasons I mentioned above, I'll probably just wait.. (and my data still fits nicely in DVDs, so no need for BR discs)
EDIT: Here is another page
that talks about blue-ray discs and Linux, see if it has any info for you.