OP, so much is going to depend on your skill as a grower and on the genetics of what you are growing. Some of the growers on here have skills honed over decades. You indicated you’ve been growing for ~9 months.
Asking “how many plants for a year’s harvest” is something you can best answer for yourself. If you’ve been growing continuously for 9 months in a 4x4 with a 480W QB, you should have a decent idea at least of what you are currently able to harvest on a per plant basis.
Not meant as a criticism, but this question plus the other thread you posted asking “when will this be ready to harvest?” both suggest that your grow game is still developing.
As a grower that has stopped and started back up a few times in the last 25 years, my yields are sometimes underwhelming when I quit growing for a while and then get back into it.
Also, trying to run 4 different strains in a single area can be very frustrating. Heavy feeders vs lighter ones, huge stretches vs minimal, big differences in flowering time between strains, etc. It is nice to have the variety though.