I think platys are cooler then Mollys too. Although there are Dalmatian and all the fancy Mollys there are some really cool platys out there like Mickey Mouse and high fin varieties.
Mollys and platys often like water a bit more alkaline but are very hardy. I have platys in two tanks with very different ph. You just have to make sure you acclimate them properly and slowly bring the ph down before adding the tetras. 6.5-7 should be fine for tetras and platys/Mollys. Unless of course they are already use to more acidic water then you don't have to worry.