Suggestions for building a lens system for 6D

i have all these lenses except the 70-200 f4 but I do have the f2.8. I have had the f4 in the past but sold it for the f2.8.

For your genre of photography my suggestions are as follows:

16-35 F4 IS - excellent quality and value for money. If you get no other lens on your list start with this one for your style of photography.

24-105 - this would be an add on, excellent lens as a walk about but that is not what you are primarily looking for. If you buying no other lens then this would be your first choice, but you have this covered by the other lenses you are looking at and you have a 50mm STM.

70-200 / 300 - I use the 70-300 as my long zoom travel lens as it is small, light and excellent quality, but it has a variable aperture. In your case I would suggest the 70-200 focal length as you could always add a 1.4x to bring it up to 280mm. Which one - well if you are never going to shoot at F2.8 then I you will not be disappointed with the f4 IS. The F4 IS is lighter than the F2.8 IS but matches it in IQ. If you do decide on the F2.8 then do yourself a favour and get the version II as it is much better than the version I.

If you want a more general purpose lens then I would consider the 100-400 II rather than the 70-200. It is indistinguishable in quality from either of the 70-200's. If you do spring for this FL then once again get version II and I would reconsider the 24-105 to fill the gap between the 35 and 100 range.

Hope this helps.