So, you don't have a 1440p144Hz monitor yet then? I'd definitely be doing that before CPU upgrade.
I'm pretty sure the PG279Q is a 600 odd quid monitor, isn't it? If so, I'd definitely avoid, you'll be able to get a great 1440p144Hz monitor for £350-400 easily. You could even get a nice 3440x1440 ultrawide monitor @ 100Hz for £450.
For SSD, 1TB makes sense to me, best value these days anyway and they can be had under 100 quid easily which is madness. 1.02TB Intel 660p seems a no brainer to me honestly, was £89.99 on Amazon yesterday(might be gone now), which is already a steal but if you keep your eye on 'em, they might come down even more for Black Friday. I'm probably gonna pull the trigger on one myself soon tbh.
Yes, your RTX 2070 is definitely fine and there isn't really any GPU upgrade that makes sense from it IMO.
For CPU upgrade, I'd probably hold on to the 7600k for now if you can. If you feel it holding you back and you can justify the upgrade, then sure go for it. If you do upgrade, AM4 is definitely the most logical option IMO, 2nd or 3rd gen 6 core and 8 core SKUs make the most sense.
However, next gen Zen(Zen3) is supposed to be out some time next year apparently. I would think that AMD would change socket from AM4 for next gen, and I have seen rumours that this will be the case- AMD themselves also said AM4 would be supported until 2020 so it would seem to make sense. If that is the case, and we're getting close to a new socket, if I were you I'd probably feel inclined to just hold on to the 7600k until you can get a 1st generation motherboard for the new socket(AM5?) which should then have multiple releases of compatible CPUs just like AM4.