I think a 5 gal is too small if you want to try breeding, especially livebearers. Is there any way you can upgrade to a 10? A 10G will allow you to breed endlers and keep up to 20 in there. Although there are reports on endlersrus.com that you can keep up to 40 endlers in a 10G tank. Of course, you'd need large water changes weekly and all.
Endlers are like miniature guppies with a lot more color blotches
Personally, I prefer them over guppies.
IMHO, I wouldn't keep more than 10 endlers in a 10g, unless there were temporary fry...