here are a few of my thoughts on the matter...
first off, not every mantid has 100 or more babies from just a single ooth.
the Ghost mantid for example, is an easy to rear, and awesome beginer mantis. expect no more then 25 babies per ooth. my avg (in the limited time that I had them) was 15 babies per ooth. there are plenty of mantids that have just a small and limited number of babies, so just don't buy something crazy like a chinese and you'll be fine.
I was also smart in that when I first got into this hobbie I "showed off" a lot of what I had to friends. they in turn asked how easy it was to care for, and thus learned at least a little bit about thier care. then when I got realy sick and had to give almost everything up, they were able to take in a lot of my pets and babies. it was a sad day to give away a lot of my mantids. but it had to be done. the good news is that they all went to caring people who at least could give them the time they needed and care for them in the way that they needed.
please also understand something. you don't have to breed your mantids.
sure it's fun, but with many here breeding almost everything, why do you have to?
like many here, I've had plenty of extra babies at times.
I prefer to sell or trade the extras when I can. I too have been free to say here that I do feed my Chameleons mantids from time to time. they are a natural food item in the wild for many of my animals. just don't expect me to feed one of my pets or feed off one of my favorites.
oh, I just got a Creo Pictipenis ooth from a member here the other day. I'm told that the ooth should have between 50-60 babies (nymphs). as a starter to get back into the hobbie, I am already thinking of just how crazy it is going to be feeding all of them. but it's not as hard as it seems. the nymphs will be kept together in a fine net cage for the first molt or two. then once I can do so they will be placed in their own deli cup and I might just sell or trade a few off to not overwelm myself with too many creos.
I'm glad you have given much thought on this topic before you started. but we are here to help in any way we can, so you'll never be all alone when a real problem happens.
good luck in what ever you do.
Harry