there are probably many more out there with more help,but here is my experience :
as far as brand I got mine at the AT&T store pretty certain I recall it to be a SanDisk and made certain it had the microsoft stamp of approvable they only had 8 gigs in stock and of course were charging what you would expect to pay for a 32 gig everything I had read and researched indicated a hit or miss on any card not officialy recomended, and most could not tell they were going to have a problem(or not ! ) until they exceeded the original on board 8 gigs that come with the phone I have surpassed 8 and have had no problems and I am finding the 16 gigs to be just fine especially since I have the free 25 gigs on skydrive.
Once the card is incorparated it becomes a permanent part of the the phones memory and can only be removed and replaced with what is called a hard reset and aditionally can not be used in any other device since it was formatted by your wp7 when installed. I did read somewhere where someone was able to reformat it by installing it in a specific older model nokia phone so it could be reused in other devices I do not recall the specific nokia but it was not just any nokia. I do not know what all you would have to do with what is already on your phone. I do know there are apps thru windows mkt place to reinstall all apps and I am sure there is a procedure to save personal data, also the phones manual and areas on microsoft specifically refer to the procedure on a hard reset.
That is about all I know on the subject. I will say I am very satisfied that I had mine installed before it was ever activated and I have had a great experience with this phone with the exception that AT&T just sits on their asses when it comes to making updates available I have had none since Mango and there is an update that Microsoft put out to them more than six months ago that addresses the disappearing keyboard many early adopters have experienced. I am hopefull the coming Tango update can not be IGNORED when it becomes generally available from Microsoft and it will include a fix finally for a problem that can cause a lot of frustation especially since you know there is a fix out there for so long, and the carrier you pay so much money to for the experience can give a rats ***. Sorry for the rant. It's a nice phone and I love the simplicity of the operating system fluid smooth and fast response.