OK in order.
1. The spawn is about 50 as far as I can count they move pretty quick :)
2. I started them on freshly hatched BBS 2 days after they were free swimming, they where fed 3x a day for the first three weeks, every 6 hours
8 am, 2 pm and then 8 pm. At 3 weeks I introduced dry food for the middle meal, I used powdered flake, crushed pellets and golden pearls. They are now in the Grow out tank and are on the same feeding schedule, BBS morning and night and dry food mid day. lights out from 9pm to 7 am.
3. I started water changes 5 days after beginning the feeding of BBS. I used an airline tube and siphoned the bottom into a clear plastic container so I could see if I had sucked up any fry and return them to the tank. I siphoned until it was as clean as I could get it, about a quart of water I would say. I made a drip bottle from a 64oz soda bottle, airline tube and an airline valve. The drip bottle is made the same way you would make a BBS hatchery only you need to put a plug in the neck that will hold the airline tube so that it can run down through the line and you regulate the speed of the dripping with the air valve. I allowed the drip to go at a drop per second until the bottle emptied and then I would refill it half way and let that drip in.
Here is a pic of the drip bottle
I did water changes every 2 days and each time I added 10% more water back than I removed so that the tank would start to fill.
4. I moved them from the 10 gal. breeding tank into a 20 gal. grow out tank at 4 weeks old.
This is my first spawn so I hope I have given you good advice it seems to have worked well for me.