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Er.. RAID is not meant to be an alternative for regular backups. It's meant to provide some data redundancy for hardware failure, availability, and speed.
A pair (or more) drives in RAID 1 with a decent controller (hardware based, no IDE RAID cards save perhaps the higher-end 3ware cards are actually hardware based, they rely heavily on CPU), shouldn't give you a noticeable decrease in speed. What usually happens is that write speed will decrease marginally (due to having to align two heads), and read speed will pick up a little bit (due to the ability of some controllers to read data bit A off drive A, and bit B off drive B, at the same time).
As for your second question you need to be more clear. A normal SCSI or IDE controller will not support hotswap, in fact it's fairly dangerous to hotswap IDE devices when the controller was not designed for it. Most controllers that allow IDE hotswap actually physically turn off the BUS for that drive before you can physically remove it. If your asking if you can have a single disk as a normal drive, sure. But they can't be used as hotspares or anything on the RAID volume.
Some RAID cards support using multiple RAID cards in a failover configuration so if the host adaptor fails it will switch over to the other one. Some even support a logical RAID volume spread across two controllers, so you can have more devices in one array.. Keep in mind that decreases your theoretical reliability by a factor of the number of cards you have.
I dunno, be a lot more specific in your question. :P
-Phil
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