Your community behavior looks quite good and normal. Its possible some of our livebearer people could comment on your pH and temp with respect to the high-fin platy but overall I don't see issues at a quick glance. WD
Neo, when it comes to using a planted tank to prevent any problems with stocking fish, maybe a picture of a planted tank would help you judge it. This is what I call a planted tank, although slightly less plants might work without first cycling your tank's filter. Much less plants and you will be looking at what MW called a tank with plants, not at all the same thing.
Your video of the platies and guppies shows mostly normal looking fish with no ich present. The only thing I saw in that whole video that might possibly be a concern is the bottom edge of the first fish's tail. I would keep an eye on that and if it becomes worse would post a picture in the Tropical Emergencies section. It is definitely not ich but may be some kind of fungal infection if the symptoms change for the worse. I try to keep my fish water clean and find that things that look like that will heal up on their own with nothing but water changes unless it a particularly virulent infection of some sort.