If you have your stock right (male to female ratios) and enough hiding places you really shouldn't have any problems. It also depends on what else is in the tank species wise.
In my experience, if the female begins to get too stressed (chased too much, bullied, too hungry, etc...) then she will spit the fry out early (free snack for others!!) or she will swallow and eat them (free snack for self!!!). You really don't have too much to worry about.
If you really want the new additions, as in want to have the best chance for survival to adulthood, then you probably want to move the holding female to her own tank until she spits out the fry...but then you have to move the female back to the main tank before she eats them (some people will actually help this process along by stripping the fry or eggs...do a search on how to do that).
If you just leave the female in the main tank (easiest way), then at the very least you will want tons of small crannies for the babies to hide in as they grow and develop, but you will likely still lose most of them. You will probably get 2-3, but it depends on so many things.
Overall, in my experience if your male to female ratios are pretty good and you don't have any killers or major bullies in your tank then you should get plenty of breeding now and in the future, and therefore you will be overrun with fry if you try to save them all. In my 125g, I started/added about 25 total fish, but by the time I broke it down after a little over a year (I moved) I had over 40, not including tiny ones, without doing anything to help the breeding. Obviously most of the babies were eaten, but I still would have had to take action to keep the tank from getting out of hand. And that was starting with juvenile fish, growing them out together, so breeding didn't even start for about 3-4 months. I also had some haps in my tank that seemed to focus and hunt the fry constantly. I actually more haps as I went along because I had over 100 fry in the tank at one point (most of them small, but still a ton of fish).