For multiple montiors - you basically just need to make sure the motherboard you pick has enough/correct connections. That will be your limiting factor.
For performance: I can't believe no one has mentioned this yet...
The NUMBER ONE biggest part that will effect casual/business computing performance is an SSD. What processor you get doesn't really matter. What matters is the hard drive. Virtually all the slowdowns in casual computing comes from waiting for the hard drive to load information into RAM. Most of your money should go here. I'm assuming he doesn't want to bother with multiple hard drives. Luckily, as a business user he shouldn't need too much storage space, especially as it's not an office computer.
(And if the touch-screen all-in ones have an SSD in them, your built computer will look bad without one).
Here's my suggestion for core components:
for motherboard, apparently the Kansas City Microcenter has only 2 FM2 motherboard models.
The cheaper one is an Asus mATX for $90 and has one DVI & one HDMI video connections, so it can do 2 monitors using exactly those connections.
The more expensive one is a Gigabyte full ATX for $125 and has one of each of the major video connectors: VGA, DVI, HDMI, and DisplayPort, making it more flexible.
Either of those should work. You an ask about motherboard deals, but I don't know if they have them for FM2 sockets. Nevertheless, I still say you stick with the A10. It's more expensive than, say, a Core i3 setup, but some internet browsers may benefit from superior GPU acceleration provided by the APU's integrated graphics.
For storage, I recommend a 500gb Samsung 840 SSD ($400). This is large & expensive, but it's the size of a standard hard drive, so no confusion resulting from two different lettered drives. (C: & D:... confusing!). And, of course, it'll make the computer seem amazing to a casual computer.
For RAM, you can get 2x4gb Kingston HyperX 2133mhz for $55 if you want fast RAM. Otherwise you can get 2x4gb Crucial Ballistix for $37:
For case I recommend a Bit Fenix Ghost ($90) for a combination of noise-mitigation & non-wacky looks:
For PSU I recommend an Entermax NoiseTaker 375w ($25) though you could also consider the Antec Earthwatts Green 350w as the Enermax has a reputation for stiff cables (the Enermax, though, may be quieter if you set the fan to the lowest setting, which is why I recommended it over the Antec):
For DVD-burner, whatever, throw in a Samsung for $17:
Total: $832 (or a bit less with the other motherboard/RAM choices)
All of those SHOULD be in stock, as I directed the Microcenter website to give me only listings for the Kansas City location (which also limited some choices, of course). Now, the price does NOT include Windows (you'll want a real legal version, likely windows 8 64-bit), or monitors, or peripherals like monitors, SPEAKERS, webcam for video conferencing if needed, microphone, mouse, keyboard, all that.
The price is also probably quite a bit higher than you'd expect. Yes, you can save quite a lot of money by, say, going for an i3 system or getting a hard drive instead of an SSD or getting a cheaper case, etc. But all the extra money is buying luxury & performance. This should be a smooth, quiet, powerful computer that will make for a good work environment. The luxuries, in other words, should be worth it - far more than they would be for a gamer.
In other words, my advice is the exact opposite of DracoMan's just above me. Yeah, you could probably make the whole system for half the cost. But in the real world, it wouldn't actually be the same system.
P.S. If you need further advice on shopping for monitors, etc, let me know.Edited by MisterFred - 12/8/12 at 8:04am