3) Transcend, Kingston, A-Data... pretty much any reputable brand will work. I would advise against SanDisk but only because they don't support high-speed mode which is supported by the custom (and to a lesser extent) official kernels.

OT: Check the Cannon website to see if Cannon have added SDHC support in a firmware update for the D50 - I'm not saying they have, just suggesting it's a possibility.

4) Yes, Nokia - search for the "Offical Case" thread around here somewhere. It has pictures too.

In future when performing "research" I suggest you try using the "Search" tool available on most forums as this will prove very helpful to you.