1. Rod--in saltwater flyfishing, at least, I think the rod is everything. My preference is for an 8wt rod that is 9ft long. Now, you can certainly fish with lighter weight rods with success, but my sense is that the faster we can land a fish, the less stress it endures and the greater likelihood it will survive being released.
I prefer a moderately fast rod for a couple of reasons. A "slow" rod creates a larger loop and larger loops mean more wind resistance and less distance. A very fast rod is just flat harder to cast for me and results in more tangles and knots in the line. I have seen very fine anglers use all three rod speeds with success, though. So, to some degree, your style will dictate your rod. But I don't think you can go wrong with a moderate speed rod and the manufacturer will provide information about rod speed in their catalogs or online.
Make sure the hardware, that is the reel seat and the guides will hold up in saltwater. Just ask the manufacturer. Most have a very good warranty, anyway.
As for manufacturer, take your pick. I like Sage but also fish a Winston rod. The TFO rods have come a LONG way and there are some very fine "sticks" provided by this manufacturer.
2. Reels--I fish Billy Pate and Ross Reels. Love them both. The Pate reels are my "go to" reels because they are durable and quite saltwater resistant. They are also expensive and take an engineering degree to disassemble and clean. I guess that is the trade-off.
Make sure the reel in which you are interested is anodized to resist corrosion and that it has a good "friction" drag system.
If you can afford a good saltwater reel like the Pate or Ted Jurasik, save your bucks and buy one. I know it is a hellacious outlay, but I have my first Billy Pate ten years after I bought it and it works as well as it did the day I bought it. Which is amazing when one considers how poorly I treat it......
3. Flyline--I use the basic Cortland 444 8wt, weight forward, floating flyline. I have tried all the designer lines, you know, and find this line works as well as any of them and for a lot less money. I like a brightly colored line because I can see it and at my rapidly advancing age, every little bit helps. These lines are very durable and don't seem to stiffen up in cold weather.
4. Leader--I am sold on the Umpqua "redfish" leader which is a monofilament tapered leader. I use either a 10lb or 12 lb test leader. You can find this leader at Cabelas, sometimes, in huge packages at an unbelievably low price. I don't use anything else.
I attach the leader to the flyline with a braided loop attachment that is made by Orvis. It slips on the end of the flyline like Chinese handcuffs and has a loop in the end through which I can pass the leader. I have never had one fail to hold and they make changing leaders a snap. Though they are Orvis products, I find them regularly at Bass Pro Shop.
5. Tippet--take your choice of any tippet material that is the same weight and diameter as the end of your leader. I attach it with a loop to loop connection by making two "perfection loops" (one in the tippet and one in the leader) and then just slipping one over the other. I prefer flourocarbon tippet because it is less visible, but I do not use flourocarbon leaders.
6. Shoes--I prefer a boot that covers my ankle and has a sole that will not easily cut. Flats booties work OK, but I prefer the flats boots that are made by Simms or by Cabelas. They lace up and cover my foot up to the ankle and above. In looking back at all the cuts on my current boots, it becomes clear that this investment has saved me many a bad oyster cut.
7. Sunglasses--I use two different pair over the course of a day. A pair of amber glasses for low light and a pair of vermillion glasses for times after the sun is up. Polarized, of course.
8. Fanny pack--I got a really good one from Cabelas that is made by Simms. Waterproof and the zipper is covered so that it is much less likely to corrode and freeze up.
9. Flies--I use five patterns (and an ace in the hole pattern) and that is it:
a. A seaducer pattern that has a very slow sink rate. I tend toward brown and tan.
b. A spoonfly. Casts like an anvil, but can be very effective when small bait fish are "flashing" or when the water is off color.
c. A topwater popping bug. Take your pick. I like yellow because it is easier for me to see.
d. The ubiquitous chartreuse and white clouser minnow. Sinks faster and has greater water column coverage.
e. A fly that resembles a small shad that I have seen referred to as the "hot flash minnow." Great, super, incredibly good speckled trout fly.
f. Ace in the hole--a red epoxy fly that is diamond shaped. I guarantee you that this fly will attract and hook black drum when nothing else on earth works.
OK, here are beginning requirements in terms of gear.
The real (or reel) secret to successful saltwater flyfishing is successful flycasting. The skill set is very different than that of freshwater fishing for trout or bass. In saltwater flyfishing, casting accurately and for distance is the ball game. So, mechanics have to be pretty darned good.
If you are interested in learning, take a class. Flycasting is not intuitive and there are some really great instructors around.
Email or post if there are any other questions with which I might help you make a purchase or if you have specific saltwater flyfishing questions.