I like to feed our livebearer fry crushed cyclopeeze flakes, crushed omega one veggie flakes and crushed peas (thawed & peeled). They'll grow to eating crumbled pieces pretty quick. A
bare bottom tank with a sponge filter (or 2) or a
HOB filter with fish net netting secured around the intake with a rubber band is how I like to go with platys.
Congrats.. they are cute little buggers and keep an eye out for more the next 5 days - the platys often drop most fry initially but there are typically a few more that get dropped up to 5 days later.