Your sydontsis will grow to at least 10cm, and depending what type your pleco is that will grow fairly large, and along with your corys the bottom of your tank is full.
Only 1 ram shouldnt grow too big and wont get terratorial on its own (as far as I know). The neons are nothing, and as both the guppies are male you can be sure of no "suprise" tank mates there.
You may be able to add a couple more fish, maybe some middle / top swimmers, but make sure you have good enough filtration for that messy plec
I agree about the neons... having at least 10 won't add too much to your bioload but improves the look of the tank dramatically! Plus they are schooling fish so love to be in a big group.