Getting back into the hobby after a 45 year hiatus. After all that time, everything has changed so much, so I'll be looking over a lot of the older posts before I start asking the same questions over again. Putting together a 54 gal community tank.
Zebra danios were my first choice, just not available. I think until the tank is fully established, the fry will basiclly just be live food.You can make it work with the mollies. Just measure for ammonia and nitrite every day or two and keep up on water changes. Do more water changes if you see measurable amounts of either. I would not bother measuring for nitrates for weeks. It will take 4-6 weeks. With these 6 fish in 54gal of water it shouldn't be too difficult to keep up on. Problem is, mollies are live bearers and the ratio you have is probably going to result in babies. My personal fish of choice for a fish-in cycle are zebra danios. I just keep up with water changes so they are not subjected to ammonia or nitrites. Eventually you will see nitrate creep up, then you gear your weekly water change so that nitrates don't exceed ~20ppm on water change day.
It's wise to keep a quality dechlor/detox product on hand for this process and for normal water changes. Most of us like Seachem Prime or Safe which is the granular form.