I disagree with Clint (hushed silence all around
)
If I understand right, your tube amp doesn't do surround sound. If so, I would get the receiver first and sub second.
A decent receiver (and you will be able to get a solid unit from Yamaha or Denon for about $ 350) will sound good anywhere, or usually can be adjusted to sound good anywhere. Pretty much ditto for the sub if you are willing to tweak it into the right spot. The Dayton unit is a very cost-effective product
http://www.*****************/pe/showdetl.cfm?&DID=7&Partnumber=300-632
Use the outdoor speakers for surrounds. They generally work great for this purpose. They are easily mounted and usually reproduce mid-range and highs the best, which is what you want in a surround speaker.
I would recommend you hold off on the main speaker replacements until you move into the new house and have the additional money. Your new place will have entirely different acoustics and speakers is one place where you are better off to get the best you can get for the specific room you plan to put it in. You're going to want to audition a couple of sets rather than be stuck with what you buy now. The Advents I listened to years ago (but couldn't afford back then) are certainly good enough to hold you over for now
If, after the first round of purchases, your funds leave you short of a more expensive choice, you might spring for a center channel. Even a lower price center like this is probably the best $ 75 you could spend for an immediate improvement (again... assuming your amp can support one) and you could always move it to another room in the new place.
http://www.thetwistergroup.com/product/DV-52CLRB%20D00812.html
Someday, you'll want all three front speakers to be from the same speaker line for the best possible sound.