I haven't cycled a tank in about 10 years or more. For this tank I did the following:
1. I bought used driftwood from tanks at my LFS and kept them wet until I set the tank up.
2. I heavily planted the tank
3. I added two filters worth of sludge to the entire tank mixed into the water and it went everywhere covering the plants, driftwood, and substrate
4. I added a bag of green water i got with some scuds
5. The tank is setup as a riparium with two anthuriums emerging
Is the water consistently cloudy, or had you recently been messing with the tank before that photo? I certainly wouldn't say from the description or photo that the tank is shrimp-ready, but presuming bacteria from the driftwood and filter sludge survive the change over you should be off to a good start. Are you adding any ammonia?
I wasn't planning on doing water changes just top ups. Is that nuts?
Yes, that is crazy talk from the care of Neocaridina shrimp side of things. I would say no if you just wanted plants and common snails but shrimp are going to do great then crash if you do that route for long. I've made that mistake and very much want to keep it from happening to you.
I was going to add about 25 cherry shrimp in about a week. That would be two weeks of cycling.
While I'm certain that is doable, I would strongly advise to hold off another 6 weeks or so. At least let the tank settle down and run clear, in my opinion.
After that the plan was to add about 5 male Endlers in another two weeks.
Fan of endlers myself. I'd be inclined to give the cherries time to breed a new generation, but it really depends on what you want. Alert fish such as livebearers will out-compete cherry shrimp 10 times out of 10. For food as well as they are really good at finding their babies.
The tank is a 20gal high with a small powerhead restricted down for some circulation and no filter.
It looks like pea soup from the photo, but I can't tell if it's a bacterial bloom (tank isn't ready for shrimp) or green water (tank isn't ready for shrimp either) or both. I would suggest at least for now a mechanical filter of some sort if you are so inclined -or being very patient before adding livestock.