I think a lot will depend on its flowering condition :-)) Mums sold for fall color tend to be very heavily budded - best to purchase them in bud rather than bloom as the flowers tend to go over rapidly. But the development of the buds into flowers is certainly stimulated by sunlight. Excessive shade may very well stunt or abort the flowering. So you've got this choice to make - a heavily budded plant that may not fully develop its flowering potential in that much shade or one already into its flowering cycle that may not produce for as long as you like (IME, a ready-to-go mum lasts about 2-3 weeks max in bloom).

I can't tell you about growing them in FL, but in NH I planted them in the fall and mulched heavily in December. I uncovered them in the spring and scratched in compost. On the 4th of July I cut them back by 1/2 and scratched in more compost. In September they were in full bud and I had lovely blooms till the first hard frost. If I hadn't cut them back in July they would have bloomed in September. I learned this tip from Paul Parent who I listened to every Sunday morning on the radio. Hope it helps.

You can still pinch or just give them a hair cut. That way they bloom in the fall when not much else is doing its thing.

We used the ITML AZM0900 Mum pot this year with good results. It has enough soil volume (4.7 litres according to their brochure) to support the Belgian Mums we grew. We had them on drip irrrigation on black landscape cloth. There was enough root that came through the holes on the circunference to keep the pots from blowing over in the wind. We plabn to use them again. Previously we used blow molded nursery containers. (Classic 0600, I think)