Looks pretty good! The moss carpet will come in. I get little moss clippings kind of 'taking root' all the time in my 12 gal. It's however patchy looking, but then again I take no time to get it to come in, I just rip it out as it's not part of my scape. I'm all for attaching it to tiles, it makes life easier.
I think you need some taller or floating plants though. Shrimp really benefit from that because you're adding vertical space for them to climb. Najas grass, amazon frogbit and other floaters work well when you have a small space like a 2.5. Also more ferns will work better than stems, because they don't grow as fast. Stems are a pain in butt in such a short tank. While najas is a stem you can just float it and it'll grow into a twisted mass of stems you shrimp will love (mine where always crawling all over it).