The K Suffix processor would be something I'd ask you to get, the iGPU is actually invaluable when you do end up troubleshooting the system. I would get the Z790 chipset over the Z690 since the Z690 boards that will most likely be available will need a BIOS update prior to you dropping the 13th Gen Intel processor onto the socket. Cream of the crop style boards tend to have the Flash BIOS option whereby you don't need the CPU or ram, just a PSU with the necessary connectors populated. Boards lower down the pecking order will need you to work with a 12th Gen processor, update the BIOS and then swap over to a 13th Gen.
To also add, if you're spending on buying something as an upgrade, get the latest though please be wary of the intermittent issues with high frequency(higher than 6000MHz) DDR5 rams while on Z790.
Are you interested in recycling your existing DDR4 ram(assuming kit)? You mentioned being on a Z170 platform hence the question, we don't know what you've got to work PSU, ram, cooler, storage and case wise.