How many minutes of 1080 video

Here you go:
http://service.us.panasonic.com/OPERMANPDF/HCV500-MUL.P...
Page 149

At the highest quality it is 1h 20m, at the lowest 6h 40m (but it says 6 hours max in one go), and at the default setting it is 2h 40m.

Page 23 is about the cards. The most important point is that the card must be at least "Class 4". It seems to support all sizes of SDHC from 4 to 32 GB, so you can check the prices and you'll be able to find your sweet spot for yourself. (And it supports even SDXC cards too, with 48/64 GB capacity if that's what you need.)

If you allow a general advice about SD cards: buy from a trustworthy source only, because there are fake cards in circulation.

Update. I was out of date about current SD card prices, so I took a quick look, and I found that a "Class 6" 32 GB SDHC cards are quite affordable (good price/capacity ratio), however, a "Class 6" 64 GB SDXC card seems to cost about 3 times than that 32 GB SDHC...