I have some questions, some may be simply because English isn't your first language - you're good at it but it does raise a few questions.
Firstly all that kit isn't a SAN, it's a lot more than that, I suspect you've just provided more information than you absolutely needed to but that's not an issue, better than not enough information. I just wanted some confirmation that you don't think that all of that kit is the SAN right?
Then there's the issue of the server - now there's nothing wrong with that server, it's a good box and the fact that it's 2U isn't an issue, they're built that way so they can take 8 or even 12 of the larger 3.5" disks - so as a LOCAL disk-based backup system I have no concern. My worry is if you put both systems in the same location, with it being a disk-based non-removable backup you're opening yourself up to site-specific outages that affect both production AND backup. For instance what would happen if you had a fire or flood and both the SAN and backup server were in the same place, you're dead right?
That's why I'd suggest you either get a backup system with removable drives and/or tapes or alternatively put this server quite a distance away from the SAN and other servers so that a site-specific problem doesn't rob you of the option to restore your data elsewhere. Oh and you're unlikely to need a second processor for that backup server, you're right there but the physical chassis is fine.
There's also another issue - two really - I, and a lot of serverfault users, HATE RAID5 as shown in your SAN. We hate it for dull, math reasons but we still hate it and try really hard not to use it where we can, preferring R6 or R10. Like smoking, driving too fast and boob-jobs R5 seems like a good idea at the time but will come back to haunt you later, often at very great expense. Please try to use R6 or R10 ok, also are you sure that your workload will be fine using SATA disks? they don't handle lots of concurrent work anywhere near as well as SCSI based disks such as SAS ones, I know they're cheaper, and they probably make some sense in your backup server - but in your SAN they may well become a bottleneck and liability.