I would stronly discourage the use of 3 subs. 2 provide more power than any man on a budget needs.
You see, the problem is that to sound good and be efficient, they all 3 need to recieve the exact same power/voltage. Since they don't make a cheap 3(or 4) channel amp rated for 150 RMS plus, you need to dink around with a 2 channel and 1 channel amp, or mess around with [ohm] numbers like the guys have been talking about, finding an amp that'* suitable for such operation.
If you want a good sound, and want people to feel you coming a block away, go with 2 subs, they'll definitely get the job done. No headache, one amp, better efficiency and sound.
By the way, your selections look fine. Typically, most brands at best buy in the same price brackets sound alike, so picking a correct brand or amp isn't critical at all. Most will suit you just fine. Buy the equiptment that looks nice (subs) and has the features you want (amps).
If you're still confused, ask one of the guys at best buy if you can see they're car. 9 times outta 10, the employees in the audio dept. have they're cars there and will show you what their systems sound like. And out of those 9, 6 of them usually run systems that are what we'd consider normal, like what you'd be sticking in your car.
If you're original intention for using 3 subs is to blow people away, literally, lol, you'll need to think about more than just 3 subs working together--enclosures, rattle solutions, more electrical problems, and how they'll fit in your car.
Hope this helps.
'95 SSEi, few electronic mods (and a stupid coupler)
HU (Sony MDX-CA680, European Ver; Sony 4x3-ways; 91, 93dB)
Yup, that'* ISU