Seedy character I get the 1st part of your post but the 2nd went over my head I know nothing about LEDs I've been gone 10 years, cob cmh??? I have no idea what that means, lol
Ok I just looked up cmh, ceramic medal halide I stopped using mh years ago because of the streach but the cmh looks different, whats the difference between cmh, mh, and hps
CoB is Chip on Board. These are typically quarter sized clusters of high intensity diodes on a substrate. High efficiency and good color output. Can damage plants if put too close. Medium penetration and spread.
Quantum Boards are groups of individual diodes on substrate slabs. Low cost, good color output, and very efficient. These too can cause light stress if used too close at full intensity.
CMH is an improved metal halide design. Most all the benefits of MH & HPS with better efficiency. Arguably better color.
For the setup you're asking of, any of those will do you just fine without going back to HPS. CMH would probably be my suggestion since you're running start to finish, but a 4000k LED would work nearly as well. CMH would likely save you a few bucks on coverage as well. Unless you are lucky, there is also usually a learning curve with LED. A lot of plants need environmental & nutrient adjustments that are different from an HPS grow.
Best advice? Find some SoG grow reports in these forums comparable to your room size and read, read, read. If you're unsure it can be easy to let someone talk you into their choice & then find out you would of preferred something else. There are also advertising partners on this site that sell good lighting supplies. Maybe check their FAQs on their home sites for specifics on power usage/coverage/color.
Good Luck!