Hi,
Wordpress for sure is a resource hog, but you can cut that down by utilising certain plugins like WP-cache, if you need I can create and message an entire list of resource saving plugins.
Regarding a suitable VPS (or for that matter, even a dedicated solution), goto
Web Hosting Talk - The largest, most influential web hosting community on the Internet and check the Hosting offers section, many premium hosts including Liquidweb are members there, and PMing some of them could get you a great custom package that would suit your needs.
Before I even get into it, let me tell you. 1000 domains is a LOT! I don't mean in the terms of domains, I used to own more than them.
But when specifically bought from the point of view of setting up 1000 different blogs, this is something you will get bored of pretty quickly!
I am telling this to you, because I have been there, done that.
Also if you plan to setup autoblogs, and adsense is your main source of income then beware, I just participated in a mass autoblog thing out here & lost my adsense account. Since adsense not being my main source of income, I was OK with it. But if at all it forms a major contributing part of your internet income, then stay away, very far away from autoblogs.
However, if you have enough man power and resources to run and maintain 1k proper wordpress installations, then I'd suggest you consult a few hosts on WebHosting talk for a good offer.
P.S - I require 1.5 gigs of RAM on one of my VPSs to sustain 100 something Wordpress Blogs with 30-35 posts each. Since Cpanel and General server Applications take up a considerable part of your RAM and Wordpress has RAM as it's favorite item on the server Menu.
Cheers