Do I Need 100 Tanks For The 100 Fry The Bettas Have?

Title says it all

 

Probably not right away. Just wait until they are old enough to start sexing and then separating the males from the females. You could most likely do some sororities with the females. Just keep an eye out for any aggression and you should be fine.

 

I keep all the fry together until males start getting aggressive, at which point I remove the troublesome males. Females can usually be kept together provided the tank is large enough.

 

Also, expect a significant mortality rate among the young fry. It is rare that 100 eggs leads to 100 fry, or that 100 fry lead to 100 mature betta. It's more like 100>50>20.
Many breeders age their betta (once they are old enough to sex/display aggression) in 1-2 gallon containers, or even cups, not full aquariums. The professional breeders overseas use wine or soda bottles that they do full water changes on daily. So you can have a few larger aquarium with dividers (better for allowing filtration), or small grow out containers that you do full water changes on daily, if you are cramped for space.
(>_> This is why I decided to not breed betta It's a lot of responsibility and work!)

 

That would seem a little crazy and I doubt you woukd be able to save all 100 of those fry. Considering not all will survive whether it be illness, growth stunt, weaker than some, fish eating them etc. I haven't bred bettas I do have three female fish, molly, and two platies thay were pregnant and though I saved 40 fry all together, I didn't save all their fry. And that's three different species of fish fry put together.