Sounds like you're leaning toward the Apple keyboard, which I like very much (the short throw leads to faster typing), but if you do decide to go with a 3rd party, wanted to add one very minor heads-up:
If you get a generic Windows keyboard from, say, Logitech, it will almost certainly work fine with your Mac--I've hooked up several with the $15 cheesy one Staples stocks. However, while the MacOS happily maps the "Windows" key to the "Command" key (which is the default keyboard modifier key, equivalent to the way Windows uses Control), the positions of the Windows/command and option/alt keys are switched versus a Mac-specific keyboard.
If you never use another Mac keyboard, this won't be an issue. However, if you do, you'll get used to aiming at the middle of the three modifier keys for Command, where on any Mac-specific keyboard it's expected to be immediately beside the spacebar where you'll be expecting the Option key.
If you want a cheap option, you might check out the budget Apple-specific keyboards from Macally, like this budget mouse/keyboard set for $27 shipped:
http://www.amazon.com/dp/B0009STJIW
(Aside: there's a reason Apple put the key there--it's much easier than hitting the far outside Control key, since you can do it with your thumb comfortably and still reach two-thirds of the keyboard with the same hand, rather than having to use your pinkie or stretch way over with a thumb.)
Almost any mouse will work; Apple's new Magic Mouse is pretty cool, but I personally use fancy button-encrusted Logitech mice myself.
A second comment on which Mini to buy: It's good advice, in general, to never custom-configure RAM from Apple since they charge so much. The mini is a special case, however, in that it's a pain and a half to get into to add RAM and you'll have to toss the 2GB that's already in it and add 4GB since there are only two slots.
Given that, and that the $200 from the base to higher end upgrade also doubles the size of the hard drive and adds an extra 10% to the processor speed, I'd personally say it's worth it if you can at all afford it. Not that you couldn't buy 4GB of RAM and a similar or larger hard drive for about $200, but you still need to install them, they won't be covered under the Apple warranty, and you don't get the processor bump.
I bought a mini for my dad recently, and despite being quite able to do the upgrades myself I went with the higher model for both convenience and value.
