Uhh…no. The bristlenose should be in no less than a 30 gallon, and that’s just for one. The comets are sub-tropicals and 4 would need at least a hundred gallons. The neons would be fine though.
Here’s an alternate stocking idea:
7 neon tetras
1 male platy and 2 female platy (instead of the comets)
5 otocinclus (instead of the plecos–add these last as they can be sensitive in newer tanks; also give them some live driftwood-helps a lot)

This is an attempt at keeping with similar colored and etc fish from your list, so hopefully it will be an okay compromise. Make sure you cycle your tank and do all your research on tank stocking, maintainance, and fish care.

Do you mean comet goldfish? If so, not in an 18 gallon and also do not mix tropicals (neons) with cold water (goldfish).

thats a little too much i would say put i bristlenose 10 neons and 1 comet