Hi! Glad to see someone who is asking questions about breeding.
I will tell you this much... You may have anywhere between 1 and 200 survive. I currently have 150+ at 4 weeks old, and most are massive in size! Soon I have to move the females to a grow out tank (luckily found a cheap one today...) and eventually the males will be jarred.
There is a ton of research, but please don't hurt your brain overdoing it. Every method is different, and every betta fish is different. Most people started out with pet store bettas... Heck, I did too! And now I am breeding better quality. Which do I prefer? Better quality. I find less complications, and plus just that extra 10-40 dollars put out on a decent pair has people lined up for fry from any spawn!
I also took in mind I am in Canada. Not many betta breeders here. Many people were thrilled they were going to find someone who could give them quality, for a decent price. I also asked around, seeing what people would like to have... In terms of colors, tail types, etc. Because of that my next spawn is not going to be a doubletail spawn, but a crowntail spawn!
And there are NO stupid questions.
If you find you have limited space, and many fry you may need to consider culling. Keep only the best of the best fry. Ones with the achieved coloring, finnage, size, etc... Sometimes it is hard, but there are times you should.
Where to sell: Like I mentioned, I asked around. Make sure you are going to be able to give what people want. 1/10 here want veiltail. 5/10 want crowntail. 4/10 want dumbos. I wouldn't breed veiltail! Also remember fish stores might take some of the fish, but not always.
Do not expect profit for the first few spawns... Between getting set up, getting live foods (I highly recommend live fry food), jars, plus getting yourself comfortable and ready for such a task you will spend lots of time and a good amount of money.
But also remember you do not need to be spending hundreds on a spawn! Think ahead! Perhaps check out garage sales, kijiji, sales in stores... Ask around, post "wanted" ads, check out second hand shops. Best of all, collect things here and there for up to a year... Rather then delving immediately.
If you need any help, ask more questions! We will help you every step of the way, if you need.