25 GB = a single layer BD-R format, the most common and cheapest
50 GB = a dual layer BD-R format, usually about 3-5x times more expensive the SL media
100 & 120 GB = a triple-layer and 4-layer "BD-R XL" format, extremely expensive (> $60 a piece) and incompatible with existing blu-ray readers and writers
A BD-R media with larger capacities than 120 GB do not exist yet.
~ 24 minutes
6x: 17-18 minutes
8x: ~13 minutes
10x: ~11 minutes
Pay a little more and get a decent media like Verbatim (not LTH!), Panasonic or Sony.