Having a spare tank saying 15 or 20 litres would be plenty big enough powered by a bio- foam filter 45, pop in some floating cambomba, pop mum in their when she is ready to explode and wait.
I went out buy a pregnant female and come home with 2 heavily pregnant platies the next morning 1 gave birth to 39 babies!!!! then other one is still very fat so hopefully more on the way.
The more natural you make it for them the less stressed they will get and unlikely to abort which is what happens with breeding traps.