SAS/SFF hard disks and ULTRIUM tape

Hi.

I need to buy a new server (the new domain controller/A.D. w2k3 server
standard in a 30 PCs client LAN).
The server has this hardware (that I don't know at all):

- the disk controller is a "HP Smart Array P400/256MB Controller (RAID
0/1/5)" (with BBWC 512 Mb expansion), with 2 x 72 Gb SAS/SFF hard
disks and 2 x 146 Gb SAS/SFF hard disks (all 2,5'' disks)
- with above 4 disks I'll do 2 RAID1 set (2 logical volumes): the
first will be C: (S.O.), the second will be D: (datas)
- the internal tape is a "HP ULTRIUM 448 DW016A" with a SCSI U320
controller

Now my questions:

- are the SAS/SFF 2,5'' hard disks safe and reliable as the old SCSI
disks ?
- is it correct to do 2 RAID1 set as explained above ? (is it a "best
practise" ?)
- is the ULTRIUM tape reliable and safe as the DLT tape ?

Thanks to all for the patience.
Rosgiof.