Respectfully, I must disagree with Mr Procaine vis a vis REI employees. I am currently a backpacking, camping, and footwear guy at REI. I used to work for Eastern Mountain Sports as procaine once did.
EMS paid much crappier wages with no benefits. REI makes the Forbes Magazine 100 Best Companies To Work For (usually top ten) every year. I am a part-timer with health care benefits, life insurance, and can split for the mountains as long as I give three weeks notice. Many of the people in my department are over 50 with tons of outdoor experience including big wall climbing at Yosemite, summiting Aconcagua (look it up), and multiple month-long backpacking trips for as long as 70 days (me). I planned and executed my first "real" backpacking trip on the Long Trail in VT (300 miles end-to-end in 20 days) at 16 years old in 1972. Tonight, I just gave the "Backpacking 101" lecture at the store and do the Mt Whitney lectures as well as ultralight backpacking etc.
Yes, shoe fit is the most important criteria when choosing footwear. Each manufacturer uses a different last. Many people previously discussed Vasque boots but they work best on narrow feet. Also, we've taken quite a few back recently with the EVA midsole disintegrating and allowing the outsole to break away.
Were I you, I'd try the Merrill Moab Ventilator in either the low cut or mid-ankle version. There is no waterproofing so they're one of the coolest (temperature-wise) shoes on the market as well as being the largest selling shoe in the world. They are very flexible with an aggressive sole tread so I would use them for day hikes. A shoe with more torsional rigidity like the Merrill Chameleon works better for carrying weight if you prefer to stay away from boots. Personally, I'm a boot man because I was a triple jumper in a previous life and have no virgin ankle tendons and/or liggies left.
Use a very light pair of liner socks and a heavier outer sock of either synthetic or wool. Use the thickness of the outer sock to tune the shoe fit. Two socks is cooler than one because you cut the boot-to-foot friction since the two socks slide against each other instead of your foot grinding. Plus, if the ground temp is hotter than your body temp, the sock combo does a better job keeping the hot out.
Cotton absorbs up to 11 times its weight in moisture so avoid it. Remember, hypothermia starts at 64 degrees with a wet body. The downside of synthetics is they get game-y after a few days on the trail. Luckily, they dry very quickly if you wash them. Of course, this does you no good if you tent mate(s) don't wash theirs.
I also teach the navigation classes as well. You don't need maps on your GPS. You can get by with a 100 dollar eTrex by learning how to navigate with the raw UTM numbers and a good map. Maps on a handheld GPS are of limited use other than the database. The screen is too small. A GPS is great for telling you where you are. The paper topo map gives you context, i.e where you are in relation to everything else (your car, the summit, the ranger station, the pizza place, etc). In ten minutes, you can learn how to locate yourself on a map within ten feet anywhere in America. All you need is a cheap GPS, a map, and a six-dollar piece of plastic called a UTM grid square. The total for all that goodness is about 114 bucks plus tax (100 dolllar GPS, eight dollar map, six dollar UTM square). I use an old Garmin 60cs with a cracked screen I bought at an REI used gear sale. There are no maps on it. The unit has limited memory.
No GPS manufacturer will tell you to go ahead and leave the paper map home. If handheld map software was so great, the military would use it. However, they navigate using a map and the method I outlined previously. I taught my wife how to do it in ten minutes. I use it to plot off-trail excursions through the Sierra and other places. You can work from the GPS to the map or from the map to the GPS for setting waypoints and plotting routes. It's navigational Megasquirt without soldering anything.
Regardless, it's great you discovered hiking and want to expand your knowledge. Your local REI has classes called Outdoor School for hands-on and boots-on-the-ground experience with a teacher. Good luck and feel free to ask any questions.