I am using the 80D Kit II (18-135), so I'm on common ground with you. My suggestion, from a practical and not technical point of view, would be:
1. If you're new to photography, you already have a good camera & lens. Experiment taking at Av mode 24mm, f/4 to f/8, ISO in Auto and you will be surprised how sharp a kit lens can be if used properly in moderate and good lighting.
2. Spending a lot on buying more lenses when you're new to photography without first learning fully with your 80D kit might not necessarily yield good photos.
3. If you can spare $400-500 after familiarising enough with your kit, consider getting the EF-S 55-250 STM. It is an excellently sharp lens for travelling to complement the 18-135. It is light and slim, excellent for travelling.
4. When your basic skills are sound and grounded, you can consider the very sharp and relatively inexpensive L lens (the EF 16-35mm f/4L IS USM) for about $1300-1400. Nowadays when I travel, that's the only lens I use. I bring my 55-250 STM for an occasional long reach.
5. When you're ready for wildlife photography (minus bird photography), say in a zoo or park environment, experiment with the 55-250 STM. When you can achieve good and sharp photos, you can then consider the EF 100-400mm Mk II but it will cost you $3000 when fitted with a good filter to protect the front glass. BUT, make sure you're ready before you take this big step because you will also need to spend $500 or more on a steady tripod and ball or gimbal head.
6. When you're really, really ready for bird photography, the Sigma 150-600mm Contemporary at about $1500 (or less) is an excellent lens to start with. You can add on a Sigma 1.4x extender and a USB dock for calibration. The 100-400 II will not give you the reach for birds. 600mm x 1.4 (extension) x 1.6 (with 80D) gives 1344mm. That, can reach birds quite well. In fact, I only use the 1.4x occasionally because auto-focusing is much faster without it. A really steady tripod and gimbal head would be necessary for birding.
7. All of the above, I've done (and more); I don't normally suggest things to anyone in Clubsnap that I've read from other sources but only from my own experience and equipment ownership because careless suggestions from more experienced members & careless buying by newer members waste hard-earned money. (Don't believe anyone who says selling cameras and gears are easy in Clubsnap or anywhere else; they are only so if you take a substantial loss, and also provided you can find the buyer. Browse and see how many unsold items there are in Clubsnap classified will make you cautious enough to only buy when you need and want to use for the long haul. It is, in my opinion, the most painful part of a photography hobby to have to sell equipment. Thankfully, I've not made that mistake so far but when I wanted to replace my equipment like selling the 550D and 70D when moving to newer camera model, each one with their own 18-135mm kit lens, they were tedious and time-wasting to sell to say the least.) Don't spend unnecessarily and don't try to do too many things, that's my sincere suggestion.
8. I did all of the above over 5-6 years. You're welcome to see the fruits of my slow but enjoyable hobby photography journey in my Flickr.com site.
9. My final suggestion for you is: Unless you've used your 80D Kit for 1-2 years, better to save the $ and learn to take better photos and find your own conclusion after 1-2 years which genre(s) you will like for the long haul and want to pursue - street photography, portraits, travel photography, wildlife (animals) or birds - then buy the right equipment for the one or two you've come to really like. You must not only have the money; more importantly, you must not under-estimate the time, or lack of it, that you're committing to this hobby. The day you decide you don't want photography as a hobby and want to earn from it, you need to consult the experienced professionals here in Clubsnap or in other forum; that's another world altogether.
Happy photographing.
PS: I only use the Canon Digital Professional that comes with the 80D and the freeware Gimp to edit my photos. I don't use Lightroom or Photoshop although I know how to use these.
PS 2: Don't buy the 17-55 f/2.8. It is a very old lens with older technology. More often than not, your 18-135 kit lens can perform better than that lens. To think you really need an f/2.8 lens is often unrealistic, especially for a beginner. For most occasions, f/3.5 or f/4 is more than enough.