Hi GIFF!!! Welcome to the world of shrimp.
Red Cherry Shrimps are pretty hardy from my experiences. I currently have some PFR (a variation of RCS) in a 10G and not much seems to bother them. Just make sure they have a decent TDS and parameters in the water and you'll be good. I've found they seem to do best in TDS between 180 and 250.
My concern here is the natural sunlight. Are you talking direct sunlight from a window or are you talking indirect ambient sunlight. At either rate if it's just java moss you really need to make sure you control the light. Java Moss isn't a fast grower and algae can quickly out compete it and take over your tank. Especially with direct sunlight! -- As a sidenote, java moss will do just fine under a T8 bulb
Is this just a shrimp only tank ? TBH on my 10 gallon I've never EVER vacced the gravel (with the exception of where I place the food bowl). It turns to mulm, mulm is great for roots for plants if you decide to add them.
The other worry here with direct sunlight outside of the algae would be the heat from being in the sun. While the shrimp do ok in temps below 80, mosses prefer temps in the mid 70s and down for the best growth.
As for the ferts, I use Flourish for my plant food as my Nitrate levels dictate. Mosses feed from the water column and no nitrates mean no foods for the mosses. Just remember if you're doing your test after using Flourish you'll see ammonia spike up a bit however this is in the form of ammonium and isn't harmful to your shrimp.
I hope this helps