Hi a4, and welcome to the site.
There is quite a lot of information regarding liquidation.com in the forum, so I won't go into to much about them here, but please do a forum search and I'm sure you will find all the answers to every question you have about them, and then some.
Tearpeak is fast becoming an absolute must have tool for marketing products on ebay, extremely useful tool to have.
Quite a few avenues to market your products online, and Craigslist is definitely an option you should consider in the mix. I'm sure you'll find plenty here that use the service, among other avenues to increase their market reach.
Regarding buy computers wholesale, that's probably a question a tool like Terapeak could answer better. It would all come down to the price you could source them for, your competition, regular market forces that play out, really a whole host of things.
It's good that you have an area of focus, all you need to do is the research to establish whether or not the avenue is going to be a viable one for you, or what you have to do to make it viable.