Hey Brown.
Welcome to the club. Can you give us an idea of the room size? It helps when considering how much "power" you need. And how loud do you want your system? Earth shaking or not? The only reason the resolution on the TV would affect your purchase, I can see, is that if you buy a 720p plasma there is no need to spend money buying a receiver that will upconvert signals to 1080p. If you have a 1080P plasma, then there is the argument over whether you will see a difference between 720 and 1080. It all depends on your screen size. I think people say that over 50 inches you'd see a difference, although there is A LOT of controversy over this as you can read from some av forums. Anyway, none of the receivers you listed upconvert to 1080p, I know that the 805 downconverts 1080i to 720p so that would work for you but 130wpc would be a lot for your needs unless you want the capabilities of running multiple zones (which the 705 does as well). I was deciding between the 805 and the 705 for awhile to power a pair of 5Ts, 5C, 4Bs, and 8D and finally decided that since I could get the 805 for an extra 50, why not just get it. Anyway my room is 12x18 and the 805 is ridiculously powerful for that size. I can't complain as I'd hate to under power the speakers. The last thing I'd suggest considering is that I've read that you should figure to spend ~30% of your budget on your receiver. Since you're spending ~1100 on speakers (minus the price of the sub), you'd be looking at ~300 for the receiver. Of course its only a rule of thumb. The largest differences you'd be looking at (I THINK) are from the 605 to jumping to the 705) in terms of HDMI (1 extra) and some of the sound processing. Maybe a guru can explain better.
Some information on resolution formatting: http://www.aperionaudio.com/AperionU/flatpanel.aspx
In just playing around with google I found the 605 for $270: http://www.accessories4less.com/make-a-store/item/ONKTXSR605/ONKYO/TX-SR605-7.1-Channel-Home-Theater-Receiver-BLACK/1.html
The 705 is $429: http://www.accessories4less.com/make-a-store/item/ONKTXSR705/ONKYO/TX-SR705-7.1-Channel-Home-Theater-Receiver-BLACK-/1.html
Keep in mind when purchasing onkyo that if you do not buy it from an authorized dealer onkyo will not back the warranty. Here is the list of authorized dealers: http://www.onkyousa.com/locations_intdealer.cfm
Hope that helps!