An alternative you may want to consider is a leg set fitted with a ballhead and a gimbal adapter. That way you can quickly and easily switch back and forth between using the tripod for big/heavy lenses and for other uses. The ballhead stays on the tripod and, when needed, the gimbal adapter fits into it. The ballhead provides the horizontal panning axis, while the gimbal adapter gives you the tilt axis.
Ballhead needs to be up to the task... depending upon how heavy a lens you'll be putting on it, maybe a medium duty (~30 lb. capacity) or heavy duty (~50 lb. capacity) model. The ballhead also should have a separate control for the panning axis (most do) and needs to have an Arca-Swiss compatible quick release platform for the gimbal adapter to be locked into. (Nearly all gimbals use A-S compatible platform anyway... they need to, in order for the lens/camera to be slid forward or backward to achieve equilibrium. As a result, you'll be using A-S plates on your lens(es) anyway.)
There are three commonly available gimbal adapters: Wimberley Sidekick (which I've used for 15+ years with lens/camera combos 10+ lb.), very similar Induro models (3 variations), and a smaller/lower capacity Jobu adapter (probably limited to around 4 or 5 lb. capacity). There are others, including some "knock offs".
Another benefit of a gimbal adapter is - because it's a "side-mount" - it makes an L-plate on a camera largely unnecessary (saving cost, weight, bulk). With an A-S compatible camera plate and a shorter lens on the camera, the adapter can be used to mount the camera in vertical/portrait orientation (rather than tipping the ballhead off to the side, which usually makes things somewhat unbalanced).
Full size gimbal heads are fine and might even be preferable for the biggest and heaviest lenses (600mm f/4, 400mm f/2.8)... But they make your tripod dedicated for "large lens use only" while installed, pretty much requiring you carry a second head for "regular use", along with any tools needed to swap the heads, if you also want to use the tripod for non-gimbal purposes.
There's a pretty comprehensive overview of the various gimbal types, models and specs here:
http://www.carolinawildphoto.com/gimbal_list.htm As to the leg set, you simply need something that's sturdy and fairly heavy duty.... How hefty it needs to be depends upon the weight of the gear you'll be using on it. Also carefully check the height, preferably without need to raise any center column. Arguably the "best" leg sets for this purpose have no center column at all. Keep in mind that to use it comfortably while standing, the tripod and head combined should bring your camera's viewfinder eyeport up to or slightly above your eye level and measure accordingly.
There are MANY tripods to choose among. Gitzo, Really Right Stuff, Nest, Feisol, Indure, Benro, Oben, Manfrotto, etc., etc. I'd recommend a minimum of 30 lb. capacity and "Series 2" size. Personally I use a Gitzo "Series 3" size Systematic tripods, which have larger diameter legs for stability (but also are heavier to haul around). Mine are older models rated for around 35 lb. Newer ones in that series are often rated for around 45 lb. "Systematic" is a term used by several manufacturers to designate modular by design... Models that can be used without any center column, although columns are available separately if wanted.
For best stability, also look for as few tripod leg sections as possible. I use three 3-section tripods and one 4-section (extra tall). Fewer than 3 sections simply isn't practical, doesn't collapse sufficiently to haul around. More than 4 sections makes things get rather wobbly... both because of the extra joints and because the lower leg sections end up very small diameter (they have to be, in order to "nest" inside the next section up).
Consider the type of leg locks used too. Personally I prefer the "twist" type because those are low profile, less likely to catch on branches, cuffs or sleeves. Lever type may be a little faster to set up, but also are more prone to wear, needing adjustment or occasional repair. The twist type are largely self-adjusting and aren't prone to wear. One minor issue with older tripods was that the twist type need to be loosened and tightened in a specific order... But newer tripods often use anti-rotating leg designs so that this is no longer a concern.
A "Leveling Platform" is an accessory I use on my two tripods that are used with gimbals (one is the Sidekick adapter with a 50 lb. rated ballhead, the other has a "full size" J-type, bottom-mount gimbal head). The leveling platform goes between the head and the legs and gives means of quickly setting the head to perfect level on uneven ground, without having to fiddle with leg length. Evey time you move the rig, the level is likely to need to be reset. With a leveling platform that can be done in a few seconds... much faster than trying to do it by adjusting the legs. The leveling platform adds about 1 lb. to the weight of the tripod, but I feel it's worth it.
I'd encourage you to spend more than you might have planned on a tripod because a good, sturdy one may last a lifetime (one of my tripods is 40 years old, another around 20 years). Plus, a tripod that you really enjoy using is far more likely to actually be used, is less likely to be left at home in a closet gathering dust!
Hope this helps!
P.S. I agree with the suggestion to shop used... I bought two of my tripods that way and ended up spending about 1/3 what it would cost to buy something comparable new. HOWEVER, you have to really know what you're looking for, to shop used.