1.) You need a RAID card if you want to build a RAID array that your mobo doesn't support. Any new mobo should support 0, 1, 5, and 10.
2.) RAID 0 will increase your speed by splitting files between drives. The risk is if one drive files you lose all your data.
3.) Depends on the RAID card.
4.) RAID 1 will make drives be a copy of each other. This way if a drive files you won't lose any data. Raid 0 is for speed as I said in 2.). Raid 10 is 1+0, which is 2 sets of RAID 0 in RAID 1. It requires at least 4 drive and will be quicker and more reliable.