There are a lot of details you can consider in choosing a shelter, so it's no wonder your head might spin when suddenly confronted with so many variables. You seem already to have settled on the idea of a full-enclosure tent as opposed to a tarp setup. That's fine. It shows you know your mind.

Of all the considerations involved, I would name as the most important one the ability to cope with the worst weather you are likely to encounter. A shelter that fails to shelter you is a disaster. The pitfall here is choosing a tent that will withstand FAR MORE than the worst weather you will encounter. The most "bombproof" tents are not only heavy, but much more expensive.

The most common kinds of weather a tent might possibly need to cope with are wind, rain, & snow. Almost any decent quality tent can handle rain (but beware of cheap tents meant for backyard use). Snow only becomes a problem with heavy snow loads. Wind is the biggest variable. A good quality 3-season tent, correctly set up and staked out, will withstand wind gusts up to around 35 mph - which is a pretty heavy wind! 4-season tents are designed to stand up to much more than that.

As for the amount of space in a tent, everyone LOVES more space in a tent. It's a luxury! It comes at a price, though. The price is weight. Bigger tents weigh more. This forum emphasizes "packing light is more fun". That's why I'd counsel you not to get carried away with getting a spacious tent.

Tent makers like to designate tents as 1-person, 2-person, 3-person. This is only a very rough guide to a tent's size. Look at floor space, peak height (head space) and how vertical the walls are. These are your only true guide to how much space you'll have.

While cost is always a factor, try not to look at cost too much. Saving $30 or even $50 looks can look smart at first, but when you are 10 miles from the road it's the tent not the money that counts.

The most tempting thing to recommend to you is a single-walled tent, especially one of the TarpTent models designed by Henry Shires. They are excellent tents, and their space-to-weight ratio is also excellent. However, single-walled tents are a bit fussier, in that you need to know what they prefer in terms of where and how you pitch them. Put them somewhere that gets heavy dewfall and you may get a brief rain shower inside your tent when you bump it in the morning. It may be that your hiking areas will be dry desert and condensation won't be a factor at all.

Lastly, if you put in a few hours educating yourself and learning the basics of tents, and you are willing to spend a couple hundred dollars, the chances are good you'll be happy with whatever you get. There really are dozens of high-quality choices out there. With luck, you might get a great tent on closeout!

Good luck!