Royce,
First, let me say I am not a network specialist, and you would get many different answers from different people and, hopefully, you will. But, I will give you my opinions. It helps that I used the ML 110 and the SBS 2003 and the Buffalo NAS and even the XP Pros plus SBS 2008 so I have a little experience with these.
6GB of RAM should be plenty. SQL will be the biggest user of the RAM and since you have 64-bit, you may want to go up to 8 or 12. But, 6GB of RAM should be fine. I actually ran a server with 1GB of RAM once. Scary.
I would question your choice of hard drives given how cheap they are now. Haven't priced them at 15,000, but I can't see how you will use an odd number without using some of the more uncommon RAIDs. (or use RAID5) Given that most IT people would suggest either RAID 1, 5, 10 or 0 + 1, you will be limited to only RAID5. Even if you used one hard drive for a hot swap or hot spare, you will certainly be unhappy. Your only option that would make sense would be to use the 3 drives in a RAID5, which would give you 72GB of usable space. A RAID1 which would use only two of the drives would give you only 36GB of space, and you will run out of room after one week. Especially with SharePoint and WSUS, etc. I would say 80GBs minimum for your system partition and if you can go double that, even better. I would at the very least get an even number of disks. I am assuming you are using RAID. If not you are right back to 36GBs for the system drive and 36GBs for data, neither of which are ideal. If you want to keep the 3 you have, then I would suggest using the RAID controller to set them up in a RAID5 for data which 72GBs would be fine. You could always add more. Then, why not get two 120GB drives and mirror them, giving you plenty of space for your system drive.
As far as the switch, I doubt an expensive Linksys managed switch with PoE which was VoIP ready but then never used the VoIP, so I spent way too much money. Linksys, which is Cisco now anyway, makes a good switch. Some argue against managed, but I like a managed switch. Just the other day, I went into it and noticed one of my computers was at 10Mbs. I then changed the NIC settings, and it was back to 1Gb.
Like the Buffalo. Can't argue with the workstations. The Star 800 printer is beyond compare. Printers should always be networked. Very nice.
I'm not too sure you will see a huge difference, but the RAM will certainly allow SQL to work better. The overall improvement in the ML350 G5 will, give you better I/O. One thing to remember is you are not only running AC but other software. I think you will be happy.
As far as a firewall, I can only recommend Cisco. I still have the PIX-501. I believe that is discontinued now. I think the 506e is still available. The ASA 5500 series is what Cisco is going with now. I would definitely get a service contract for at least the first year. The ASA's also work with SPAM, malware, viruses, etc. As far as things like Barracuda, I have never used them, and I know they are pricey. I love Cisco, but that is just I.
If it maxes out at 16GBs, then I would go with 16GBs. I doubt you will need that much, nor will you likely notice a huge improvement, if any, if AC's performance. I have 20GBs, but then I love toys.
Personally I wouldn't get all bogged down with access speeds and the fact that RAID1 has slower write but faster read times, etc. Again, as mentioned above, three drives are not optimal for a RAID setup. I would recommend buying at least a fourth drive. If you bought the same size drive, you would have two options that I think are feasible. You could set up a RAID 5, giving you 108GB of space or you could set up a RAID10 and get 72GBs. You could also set up two mirrors without striping and have two virtual drives instead of the one RAID10.
You could also buy a 5th drive, and set up a RAID10 with a hot spare which is better than a hot swappable drive if your RAID controller supported it. Still 72GBs. You could set up six drives as a RAID10 and get 108GBs and have another drive for the hot swappable. Finally, you could go RAID5 with five drives and a hot spare or six drives all in the RAID. In all the RAID5s it would by Total# of drives minus one drive times the size of the drive for total space. With the RAID1 or 10 it is simply half the amount. There are so many things you could do. You could do a RAID1 for your OS and a RAID5 with either three or four drives either leaving one bay open or adding a hot spare. A hot spare is nice, because if you lose a drive it pops in instantaneously, then you swap in a good drive for the hot spare. No matter what you need more drive space.
Personally, I would put redundancy over speed and efficiency. You have the backup with the NAS, but you also need more space and a good RAID. Remember, RAID5 is cheaper, but RAID10 will give you the most redundancy.
I probably got a little out of control with the RAID. I would be more than happy to go over it with you. You first have to ask yourself how much space do I want for my OS and how much for my data. And, it is imperative that you have at least a partition for your OS and a separate one for your data. Personally, I like to have at least four partitions, one for OS, one for data, one for installs (key) and one for temporary backups especially with backup programs which allow two backups to be made at the same time, e.g. Backup Assist or Acronis. Microsoft still hasn't come up with a good backup program.
