Speaking of guitars, think of how you are going to get to the right signal levels. If you use an external preamp anyway, a good line level IO should do. Personally, I´d look for something with XLR connectors for balanced signals. That way, studio use or longer cables in a live setup are taken care of. Vermona TAI or ACL Audio Interface come to mind.
For effects, it depends on what you want to achieve. There are modular versions of well established pedal effects like the Strymons. To get more on the crazy modular side of things, Noise Engineering have a very versatile platform with their versio series: You can swap the firmware and change the module into a delay, reverb, distortion etc. The frontplate is labeled according to whether you buy it as reverb, delay, etc. but there are overlays available as well (either for specific firmwares or neutral "1,2,3...").
For every "cool module hp" plan 1-2 hp of "helper modules" such as multiples, mixers (audio and cv), vcas, polarizers, attenuverters etc. I like the Happy Nerding ones for their great build quality and use of dual pots (inner and outer pot, so 2 in the space of one). Probably throw in one or two EQs to adjust signals in between modules.