Just got a 4-bay Nas server, need advice please

I Just bought a Verbatim 4-bay power bay nas server, but I dont know a lot about nas servers. I have 3 MED400X's and a MED500X, as well as a d-link DSM330. I will have to get an ethernet switch as I just haven't got enough ports, so my questions are :

1. Advice on a switch - my router is a D-Link DIR 655, would I be better getting a D-Link switch? I was thinking of a DGS 1008D
2. Hard-Drives. Can I take the hard-drives out of the enclosures of my USB hards drives (2 x 2TB + 1 x 1.5TB) and place them in the powerbay?
3. Ethernet cables. Is CAT6 better than CAT5? Will it work ok with the Mede8er's (One cable will have to be about 60 mts long)
4. R.A.I.D. I dont know anything about it, so any helpful tips will be appreciated.

Thanks