Welcome, Kathleen.
Don't feel obligated to get a VP150 in that size room; I have a VP100 in a very large room and am quite happy.
I would definitely start with mains+sub, especially if you watch a fair number of movies.
I have heard neither the EP175 nor EP350, but conventional wisdom around here seems to be that there is a very significant difference between the two and that the EP350 is worth the extra money. The wide openings you have into other rooms would probably warrant the upgrade. Depending upon what you want, where you live, and how important it is to you to have the finish on the sub match the finish on the mains, you might also entertain the notion of a sub from another quality manufacturer.
My opinion on the overall setup matches Dr. House, although if you can spare the extra money, moving from the QS4 to QS8 might be a consideration. Personally, I'd rather have the QS8/VP100 than QS4 and VP150, especially in that size room. The QS8's have a deeper bass extension that you might find valuable with all kinds of content.
People love Denon receivers. Although I have owned them in the past, I've never thought they were a particularly good value, and the manuals and remotes are just horrible. Some people I trust and respect have reported reliability issues with Marantz. I am currently running an Onkyo 805 and am happy with it. I also have an older Onkyo still chugging away trouble free in another system. I think they provide pretty good value nowadays.
Don't let these guys try to talk you into an expensive receiver. Just get the features you think you need/want. Many units in the $400-500 range are amazingly capable, and you don't need a retarded amount of power in that size room.
If you don't need pre-outs, zone2 or seven channels, the 4-HDMI, Audyssey-equipped
refurb TX-SR507 at Accessories4less is a bargain for $269. They also have the 607 for $100 more.
Another good place to check is
http://www.shoponkyo.comEnjoy your journey!
