LOL your got a loverly fish there
Firstly the thing to remember is these fish are a nightmare to keep, as soon as the females drop her babies she will turn and eat them.
Growing masses of java moss will help a great deal and and old trick is to use a gold fish bowl, as the female will corner the fry and eat them, so a bowl wit5h no corners and masses of java moss in it can give their fry a chance to survive.
When pregnant these fish dont put on much weight unlike guppies, so what u need to be able to do is view her from above, when she puts on the slightest amount of weight she's very close to dropping.
A 4ft is a big tank for these, their be just as happy in a 2', as for mixing then there is little you can do, any other livebearers other than hardy goodieads will never be happy although
Priapella should be fine as them from similar locations.
They love the surface area's mainly and like a good turn over of water as their from rapid flowing streams,
Foods, quality flake foods are fine, but they love blood worm, grindel worm, dapina and brine shrimp.
Anything else?
P.S. fine a photo on the link below
Fishark pages
Also check out David McAlister at the top he's the UK leading colector and breeder in barcy's and Xiphophorus