1.) Don't use software raid. Use server orientated hardware (server board, reputable raid controller)
SME does support hardware RAID, but it's software RAID is really fine for the intended purpose.
2.) SBS can work and prolly will considering you don't need a large license volume and nor huge RAS requirements (load balance, fail-over, etc), but I would highly recommend a strong firewall between the server and the WAN.
SME is a brilliant firewall. Redundant PSU (buy a spare hotswop unit) and Raid 5 + hotspare do come to mind if you don't want to worry too much about hardware.
3.) UPS is needed if you like your exchange. A generator is a bonus.
UPS yes, generator = overkill.
4.) Make a decent active directory group policy that will lock down certain parts of of the domain pc's. (can even change "My doc's" folder to be automagically mapped onto the server)
Dude, simplicity is the answer here. SME automatically creates a mapped folder for each user, you can simply change the properties of My Documents to point there. Although then if you're away from the office, your docs will be left behind.
5.) Please put a little bit of structure into active directory. This makes life easier when implementing policies, restrictions and so forth.
6.) Write down the way things were setup, including passwords and store it in a safe.
Always a good idea.
7.) Backups! maybe get an RDX (HDD) device, tape or similar to do regular backups (store recent locally and previous off-site, or make duplicates for both... had enough of customers crying cos their stuff did borked) -- The techie you get in will look at you and say something like "Eish! sorry for you!" when things go pear.
You can setup and extre SME box to replicate to, but in most cases a USB drive with a scheduled backup (SME does this too) is fine.
8.) Maybe install SUS so windows updates are only downloaded once. Get some corporate antivirus as well (email and flash drives are ev0l)
Antivirus on the desktops yes, SUS no. You don't want ALL the Windows updates on your desktops, trust me. Rather download Autopatcher and deploy them manually once a month, and only the really critical ones. Windows updates will slow your machines down over time because of all the rubbish it installs. I've seen this over and over and over. SME has built in virus scanning for the server and email, it does not however have enterprise wide deployable AV like the Trend products. I think there is a contrib that does this though, havn't tried.
9.) Don't touch the server unless it is really sick. Lock it up in a room, cage, anything that will stop the evil minions from believing that the mysterious box in the corner is a toy. PS, you still want to hear the alarms on the server when a drive/psu is feeling sad and air-conditioning/comfortable environment not only makes people happy, but servers too.
Agreed. your SME also will not need a screen keyboard and mouse, except at install time, so lock it up somewhere - with proper ventilation of course.