Caz, if your pH has been holding with the 7.6 then I really think you're going to be fine with the platies (and honey's was it?) In your particular case I just don't think we're dealing with fish that will have mineral or pH needs that call for special attention beyond good weekly water changing habits.
To try to answer another question appearing in the last few posts, its quite true that livebearers in general prefer harder water (more mineral content) whereas south american fish (tetras, angels, lots of others) prefer softer more acid water. BUT, these prefs don't necessarily rule out all fish in cases where the water conditions are reasonably neutral overall. The way I would describe it is actually that the majority of common trops we keep get along in a wide range of conditions as long as they stay reasonably stable, whereas there are a few species where we like to pass around special notes and be aware of their individual quirks (like GBRs needing really well-kept water for instance.)
For those who get interested in going deeper into pH, GH, KH and those topics, I've written lots of very long posts way in the past with long writeups about these, including the article with Robby that his sig has a like to. OM47, Bignose and Neale also all have important writeups here and there on these topics. But again, in Caz's case, I don't see a need to get bogged down in these things for now.
~~waterdrop~~