Some other things to consider
Think about how much RAM you will want eventually, and whether you feel comfortable opening up the Mini yourself. The good news is that 4 gigs in the higher end model is probably enough for almost all uses. Also, you can get the lower end model upgraded to 4 gig by someone like MacMall at the time of ordering for about $150 (to do it yourself would cost about $100 for the RAM, and you could probably sell the old 2 gigs for about $35).
Otherwise, if you do it yourself, it can be disconcerting for several reasons. First, you are doing something that was not designed to be done by a consumer; second, the "cracking" sound that the tabs make when releasing sounds like you have just destroyed at least the case of your brand-new toy (probably not, but it sounds that way); and, third, because if you make a mistake and damage anything, the damage is not covered by warranty. If its the logic board, the cost will be at or near that of the new computer.
Second, don't expect BluRay support from OS-X. Even with an external drive. OS-X doesn't support it, and none of the rumors preceding the WWDC are suggesting that will change. You can install Windows and it will support BR, but if you're doing that, and the small size of the Mini is not a critical issue, you can spend less money and get twice the computer by getting a PC.
Consider getting an external drive to use as a Time Machine backup. It works great and gives you hands-off data security with little or no performance impact.
I too had issues with the Magic Mouse when using it for a home theater PC (alongside me). When I moved it to a desktop computer my hand position was not painful as it had been. The functionality is nice. I agree with the recommendation that you spend some time with one first.
Good luck with your purchase
