Way more plants than you need under the 300W. I'd grow about four, hoping for a 50-50 split on the female/males. One or two plants will be plenty for a scrog. Personally, I don't waste my time on non-feminized seeds.
I'm doing one myself, see my diary here:
https://www.thcfarmer.com/community/threads/indoor-mini-grow-top-fed-dwc.90641/ I'm running a 600W plus a 300W Higrow panel, will be growing two plants.
Sadly, I think you'll be disappointed with the 300W light for the full crop. The plants will grow, but the light's coverage area will be very small. If you can, I'd double or triple the lighting. I'm pretty pleased with the results of my combo, though the plants will tell me if my perceptions are correct. With the 600W plus the 300W, I'll be getting about 44 watts per square foot (3x3 growing area, 250 watts at the wall for the 600w, 125 watts at the wall for the 300W). Thats enough to grow well.