Ryan, there's been some good info given so far. I'll add some things that others have passed on to me and a few things I've picked up through experience.
* First, and I think most important in your case, five is a big number of hunters to satisfy when expectations are high. I would suggest that before feelings are bruised and friendships suffer, that you guys have a serious talk about the fact that this isn't deer or hog hunting, mistakes are going to be made and you're there to learn and have fun first. I guarantee that someone in the group will end up feeling slighted over minor matters if details aren't ironed out beforehand.
* You say you'll be operating out of a base camp. Assuming you mean near the vehicles, then you can take as much as you need to be comfortable, and I would suggest doing that. Camp comfort, conveniences and good sleep will help you hunt harder and ease some of the potential stress from point #1.
* I have taken two different packs in the past, but settled on the "do-it-all" pack. I can carry everything I need for 2 weeks of packing in, setting up a spike camp and cinching the pack down for use as a daypack. Since you're going to have more room at a base camp, finding a cheaper used freight hauler may be the way to go if you like your existing pack as a daypack. Don't obsess on what may be the perfect combo - that will vary by hunting situation and you will learn a lot your first time out about what your needs and preferences are.
* Other gear: unless you're a gear junkie, don't worry about having the latest, greatest, lightest, coolest anything. Elk don't care about your camo. Water doesn't care how it's purified, fires don't care how they're started. You get the idea.
* Navigation: I don't have a GPS. I've used topo maps, a compass and many hours studying topos and aerial photos of my hunt areas. I've only gotten turned around once and had to spend one night on the ground.....kinda exhilarating! I am thinking about getting one of the apps for my phone this year and downloading the maps of my area to use offline, but I have more research to do on that. My partner has a GPS, so that'll help me make it back to camp.
* FIND FRESH ELK SIGN BEFORE YOU HUNT! One thing I've learned is that with a limited number of days to chase them, it is best to find them first. They can, and often do cover a lot of acreage in their daily comings and goings. Way more than whitetails, generally. My first couple of elk hunts I spent far too much time hunting right away. I've since learned to find them first and then strategize about how to get within shooting distance.
* Other than talking, noise doesn't seem to scare elk off until you're in shooting range and they can't locate another elk. I've had several elk, both cows and bulls, close the gap on me just from hearing me walk on game trails or through the timber. So you do need to keep your eyes up. I mostly hunt dark timber and I'll walk a ways, stop and watch for a minute then glass a bit. If I don't see or hear anything Ill pick my next stopping point and move pretty quickly to it. You'll be shocked when you see how fast elk move through blowdowns and on steep slopes. They are used to hearing the sounds associated with faster movement and it doesn't seem to alarm them.
* Calling: I've had various degrees of success calling with cow sounds and bugles, but am not confident enough to give much advice on it. There is a bunch of info out there to be found and I would suggest you learn some basic stuff and practice. The best results I've had is 1) simply mimicking what sounds I hear them make and 2) making as weak a sounding bugle as I can when a bull bugles near me. They seem to want to come kick the little guy's butt. I know a lot of guys that are after bigger bulls have other tricks up their sleeves, but I haven't put the work into that yet and I'd be happy with any elk that isn't a small calf.
* Time: hunt as many days as possible. We're allowing for up to 11 days this year. I won't plan for less than 10 again. You can easily spend 2 or 3 days trying to find elk and if you have to relocate you're already down to just 2 or 3 more days if you just have a week total. Since we have to travel so far to get to them, I want to maximize my time in the mountains. My longest trip was 18 days and was spectacular.
* Be prepared to hurt. Be prepared to hunt tired. Be prepared to push yourself past previous levels of physical comfort. Mostly, be prepared to be mentally tough enough to endure those things. I've had 3 elk hunts where I was wet most of the time. I no longer believe in waterproof boots and have just accepted that I will be hunting with wet feet.
* When you find where some elk are bedded, don't blow them out of there by going into their bedding areas or letting your scent reach them. They will find another drainage to go to ASAP - and it won't be the next one over. Pay attention to the thermals and find a likely ambush spot where you think they may be moving to next.
* Trout: If you're going to be near any small streams, consider taking a little fishing set-up with you. I take a length of fly fishing tippet equal to my arrows, with a bead head nymph tied to it. During the middle of the day when the elk are bedded, I'll pull out a nock, place the thicker end of the tippet inside my arrow, replace the nock and I now have a small "cane pole". I'll sneak behind a rock or tree and jig the nymph into a dark pool. I usually catch 3 or 4 little cutthroats this way. I'll start a little fire, gut the fish but leave the heads on and then hang them over the fire with a green twig. In just a few minutes I'll have a tasty shore lunch that helps break the monotony of bars, jerky or granola. I usually take off my boots, let my feet air out and maybe take a little siesta as well. This really gives me a little boost and makes the afternoon hunt much better.
* Take a stumping arrow or two. You'll be amazed at how different the mountains feel when shooting. Our flatland perspective needs an adjustment. Plus, it's just fun to shoot - another midday break from hunting hard.
* As others above said, HAVE FUN!
* Deer hunting from a tree stand may never be the same. It isn't for me. After my first elk hunt all I wanted to do was go back to the mountains. It is so addicting that it is dangerous!
I'm sure I've got a lot of other stuff to share, but this post is long enough. You're gonna have a blast and not gonna want to come back to Texas.