1. I do have an Indian Almond Leaf in the tank and have seen shrimp on it. Also, quite a few plants and driftwood. Algae has decreased substantially. Do I need to feed anything else? I may add a slice of cucumber or spinach from time to time, but do I need to add anything else to feed them?
From my own experience, I personally would not put any vegetables in there. I blanched a zucchini according to a website for RCS and no one- not the RCS or the ghost shrimp would even touch it. (Zucchini was the member's favorite vegetable, followed by carrots.) I tried for probably 1.5 to 2 months on this vegetable idea and the only thing I got was a mess when I took it out 24 hours later each time. Eventually, I stopped and all involved are happier.
On that note, I will say that these RCS are the best cleaning crew in the world. I have probably a 3:1 or 4:1 ratio now in the 10 gallon tank of RCS to ghost shrimp and algae and dead leaves of plants are now a thing of the past. They do poop a lot, but I vacuum that out during my weekly water change (50%) which leads me to your next question.
2. My nitrates seem kind of high for what I'm seeing are ok for shrimp. I've tested almost every day this week and early in the week was up to about 30-40 PPM, so I did a probably 30% WC. This brought it down to about 20 PPM and that was on Tuesday. Since then, every day it is staying at 15-20 PPM. I was hoping that with as much plants as are in there, they would be consuming some of the nitrates but it doesn't seem to be happening. I did another WC tonight of about 25-30%, but it really didn't affect the nitrates much. I have only put in some Thrive once this week because I'm afraid that if I don't, the new plants are not going to establish. It seems that smaller water changes and less frequent are what I need to be doing with a shrimp tank, but it's not reducing the nitrates. I may be overthinking this, but I need help!
This is something I struggled/struggle with as well. I did make a posting about it (HERE, again, if you want), but there were no exacting answers or results from that. And honestly, I continued to struggle with this. Eventually, I thought about it, though, and if the shrimp can survive (and multiply!) in this DC water which (now) has 5-10ppm nitrates and goes up for some magical reason in my tank to 40/80 (I can't tell the difference), I will accept that. So, I continue to do 50% water changes every week and everything is hunky dory.
Also two comparison notes- (#1) I don't use any chemicals or fertilizer in the tank except prime when changing the water. (#2) I don't have a planted tank. Just gravel at the bottom and all of my aquatic plants are free floating. I have lots of pothoses rooting/growing in there as well, in the hopes that they will suck up nitrates, but that still doesn't seem to be the case.
Now, the interesting part- at least in my mind. In the past couple of weeks, I decided to add about 15 ember tetras in this tank. Before adding them, I did a water change and cleaned two of the three filters I have. (one of these and one of these LINKS FOR BOTH) Nothing fancy- I just squished the sponges in the waste water and shook the bio media in the waste water as well to rid if of any loose sediments or plant gunk. The next day, after acclimation, I measured the nitrates. These had actually gone down to 10/20! It was not enough time for the fish to have much of an impact, so I am guessing that maybe there was lots of gunk/stuff (?) in the filters making nitrates. The next water change, I did the same thing with the third filter (a green sponge one) and so on Tuesday, my water change day, I will see if all three filters being cleaned helped bring the nitrates down. I've never read about this happening before, but hey, it worked, so I'm glad.