How does one even begin the agent research process?

The book is done. It is on to the next steps. I've spent the past couple days scouring agent query and query tracker for information.
Oh my heavens there is a lot of it.
There are so, so many agents out there, and then the ones outside my genre. I'm starting a tentative list, but its hard to differentiate between the ones that would do great and the ones that would be perfect, if you know what I mean. I'm new to this whole thing, obviously, and its fascinating and a bit complicated, though that's okay. Live and learn, right?
Really what matters is that this is a two person decision, so what I expect my job to be is make a list of agents and just keep submitting until something good happens. I've heard seven at a time is the magic number. And I think I'm over-analyzing things, too, because if I can find someone who is as passionate about my project as I am, then that's really the main thing I'm looking for, right? I'm one who believes that everything happens for a reason. My job: submit and deal as smartly as I can with what happens.
Right? Any advice? How do you find agents you think would be right for you? And what kinds of questions should I be ready with? Though I haven't done specific agent research until recently, I've done lots of reading on the whole agenting system and contracts and all the uproar and controversy around that, so I'll try and be as wise about this whole thing as I can. But...help?
This is all still a bit in the future yet. I've got editing to do and beta readers to give to and more editing. So couple of months, ish. We'll see. But I'm going to start working on a query letter and put it up here for your advice and critique in the next little while.
Agents. Ah!!! 
Sarah Allen
p.s. Also, I mentioned Downton Abbey yesterday. Oh. My. Gosh. Why must the BBC be so freaking delicious? Its quite taken me over lately, case you couldn't tell.