Small token gifts are nice for people who do special favors for you, as Cubans frequently do--the casa host who calls ahead to reconfirm your lodging in the next place on your itinerary, the taxi driver who makes extra stops for you along the way, the kid who takes the trouble to help you find an address. But not a good idea, ever, to hand out things at random, and never EVER to children on the street, as it just encourages them to beg from tourists. Yes, baseball caps are good gifties, as well as being a useful clothing item in such a hot, sunny climate. Incidentally, guides in national parks earn tiny, tiny salaries, and most of them do enhance a walk with the information they can offer on flora, fauna, history, etc. so a tip in money is appropriate for them.
The mogotes (mountains) around Vinales are weird--they stick up out of flat terrain--tobacco fields and the like--like the hump on a camel, so it is possible to hike in that area on relatively flat terrain. I don't know the trails in detail, but know there are some on level ground. Your casa host should be able to find a guide for you who can tell you how smooth they are. Generally speaking, I expect they're not as well maintained and smooth as what you would find in a US national park. Cuban parks just aren't like that.