Leaving the male with the fry vary from male-to-male, with some of mine I remove the male once the spawning act is over and others are still with their fry today after 3 months-the longer he can stay with the fry the better, but if he is eating them, well-you don't want that...lol-also, often the first spawn from the female you can get old eggs and the male eats them and it take a second spawn from her to get fresh eggs...I usually wait at least 3 days between spawns on females if well conditioned to start.
I feed fry-infusoria and newly hatched BBS-once the BBS absorb their yolk sac they have little nutrition and you can see sudden death problems
I would set the BBS hatchery up 24 hours apart and hatch small amounts at a time feed within 24-36h of hatching them-I usually start hatching BBS when the fry are about 4-5 days old-but I also have mature tanks full of micro organism for the fry to eat once the fry absorb their yolk sac at 72-80 hour mark
To convert 81 liters is 21gal...right.....that should be fine-how tall or deep is it? I spawn in 10-12 inches and use lots and lots of live plants as a natural divider for the female to prevent premature egg drop. I also use lot of common snails as part of the clean up crew and for infusoria development a great first food for the fry ( you know the fry are eating infusoria from the black dots in their stomach) what fry food do you plan
Getting the female conditioned is really important to get quality eggs (I am sure you know this already)
I would move the whole spawn to the bigger tank all at the same time and remove the over aggressive ones as you see them.
Females usually pick the dominate male and they line up to spawn with him-the less dominate or more passive males sit back and stay out of his way so not to make him mad and he kicks their back-side....lol......sometimes the less dominate males will not fin out very fast/good and will maintain shorter fins...not all but some do.