The lens you have is an excellent one; the following Canon lenses are all really good (they are also heavy and not inexpensive): EF 11-24mm f-4L USM, EF 24-70mm f/2.8L II USM, EF 70-200mm f/2.8L IS II USM, and EF 100-400mm f/4.5-5.6L IS II USM; the EF 100mm f/2.8L Macro IS USM, and EF 50mm f/2.5 Compact Macro (inexpensive and light) are both very useful, if you want macro. The Extender EF 1.4X III works well with the 100-400 and the 70-200; I understand the Extender EF 2X III is great with the faster zooms and the primes.

You have to decide how you want to take your pictures--there are really excellent primes available, but the zooms offer more flexibility at the sacrifice of usually only one stop of speed. Your new camera is supposed to be great in low light, so a slightly slower zoom is probably not going to limit your photography; the f/4 zooms are lighter yet and less expensive. I think you are likely to be happy with any of the Canon L series choices. Many who post here swear by their third-party lenses, especially the 150-600 zooms.

I had three primes with my film cameras (and finally, a zoom). It was always a frustration to need to change lenses when I needed a different perspective (especially where it was inconvenient to swap); it was also frustrating to settle for a picture that would have been better with a different focal length than I had. Now I have zooms that cover focal lengths out to 540mm (with the extender). I cannot imagine ever going to primes again--I take mostly family pictures or travel pictures, and the flexibility to frame or compose with a zoom is far more important to me than one or two stops of speed; if I move to more portrait photography or some other studio work, I might find a prime useful, but both the 24-70mm and the 70-200mm are great for portraits, too. The only problem is knowing which zoom to pick when touring a location for the first time (of course, you can just carry as many as you can handle). When trying to get wildlife, the longest lens is always the choice, if the light permits; Canon's super telephoto primes are quite heavy and expensive, and you should definitely try before you buy one of them (rental or try a friend's).

So, like the answers to most of the advice-seeking inquiries here. it depends...

Of the over 15 lenses I own, the lens that I use the most is my EF28 to 300mm f3.5 - 5.6L. This is my go-to lens for everything except wildlife and sometimes in thick woods I mount it on my 7DmkII. It is a very versatile lens and the build quality is excellent. I have shot in the rain and snow with it without a lens jacket and have had no problems but use a jacket as not to tempt fate. While it is not as fast as the 24 to 70mm and 70 to 200mm lenses, which I also own, the ability to go high ISO compensates for that shortcoming. The advantage over that pair of lenses is that the 28 to 300mm covers a greater range and you will not have to change lenses to get that range although sometimes I do miss the 4mm at the wide end.

I find the 28 to 300mm good for wandering around without a specific subject in mind or 'gun and run' shooting. I can move from group shots to individual portraits effortlessly and quickly. I have used it for landscapes and urban photography all over the world and rarely found it lacking. It is not a perfect lens but it is pretty close.