Are you thinking of SBS 2008 Standard or SBS 2008 Premium? The Standard Edition does not come with SQL, so yes Express will be more than enough.
You would not want nor would it be feasible to take home swappable hard drives. Swappable hard drives are a function of the server in that it allows you to put hard drives in from the front and the drives which generally have special pins allowing them to connect and be grounded simultaneously. While they can be swapped out to bring different data to the computer, their main purpose is to replace a failed drive in a RAID. A truely hot swappable drive can replace a failed drive while the computer is still running.
A hot spare, which is probably better and can be combined with hot swappable drives, is a drive which is already in the machine, but is not being used. It automatically replaces the failed drive behind the scenes and the RAID is rebuilt giving one plenty of time to replace it.
Taking a drive home from the computer is not your best option. The drive would probably be a 250+ GB drive which you would be using for a 50MB backup. What you would probably want to do is have two portable external drives and alternate taking them home. Many would recommend simply purchasing one or two 4GB thumb drives, but make sure you encrypt the data first. The .enc file is obviously encrypted, hence the extension .enc.
If you aren't using RAID (which is one of the main advantages of having a server with many hard drives), then hot swappable drives and hot spares aren't very functional.
The T410 is a very good choice. If you go with SBS 2008 Premium, it comes with a second server and you can run both 32-bit and 64-bit. This is because Exchange can be run separately. The Premium version usually runs about $800 more than the standard version.
SBS 2008 Standard must be 64-bit as it contains Exchange Server 2007 which must run on a 64-bit OS. Given the fact that the 64-bit OS has many advantages and everything is moving that direction, I see no reason not to use 64-bit. You will be glad in the future. 4GBs is a lot of RAM (in fact it is the minimum amount to run either), but with 32-bit, you are forever stuck with 4GBs. You may never need more, but you never know. And, with 64-bit, you can go as high as 32GBs, which is the limit for SBS 2008 Standard. As you mention, there is really no reason for a different SQL server, but it doesn't matter with only 4GB as Workgroup edition takes up to 3GBs and Standard and other editions are limitless.
Amazing Charts as you say, will run very well on the SBS. Of course, if that were the ONLY reason to get a server, then it would be overkill, but it will definitely do well on the server. The main thing is that no one will be using the server, and a server is designed to run many days without a reboot. They are very stable.
HTH. I am glad to help, and my experience has been pretty much with what you are looking at. I have only worked with Windows Server 2000, SBS 2003 and SBS 2008 and used both 32-bit and 64-bit OS. I am fairly familiar with SQL Express and Standard and have used Exchange for over four years. If you have never used SBS, you will love SharePoint and RWW.
