I dont have a hub but can I just connect both of them to my computer and when I'm done backing up just disconnect one?
If what you're interested in is data protection, then yes disconnect your drives when done.
Part of the danger to your data is from power surges from your computer, or virus, trojans, etc. This can't happen if your drives are disconnected.
This is also the advantage of an external drive, compared to backing up to an internal drive. Make your back up, unlink it and power it down. Thing is, you have to remember to plug it in every few days when you do a new back up.
If you are going to be redundant and use two backup drives, I would play leapfrog and back up to one drive today, then the other drive next time, etc. If you happen to pick up a nasty virus, you should have a clean backup.
I would stay away from external RAID arrays unless you are cramped for space and need something like 3 terrabytes of storage. RAID simply gives you more chances of your storage to have a failure. The cost of RAID on top of several drives means you are paying more for the same storage.
Backups that use some form of compression allow you to keep lots of data or multiple backups (ie one from this week, one from last week) but there is more chance of corruption and losing a file. I have had the situation where my compressed backup had a corruption in the file system and the whole thing was FUBARed. Best backup is non-compressed, if you have the space for it. It is also faster to make.
How often to make a backup and how many to keep depends on you and your data. For example with my photos, if I lose photos I took 2 days ago, I'm not usually that upset. I can retake most of them, set up similar shots from memory, go to the same location, etc. The kids are just as cute today as they were on Wednesday. There is no way I can replace shots from last year though.
Same with anything I've written or researched. If I redo it, I'll probably do it better. But I could never replace the body of what I want to save from over the past years.
Things like music files, movies etc. I could replace them all, but it would take months to replace what I've built up over years. But something I encoded or downloaded Wednesday is no big deal to replace.
So for me, once a week is fine, and if I have to replace anything I did in between I don't care that much. You have to be your own best judge.
It can be well worth it to keep a full disk image which can quickly replace your entire OS installation and installed programs, drivers, updates, etc. I would keep my files separate though, and do a fresh backup every week.