Those all look too early to tell right now. Most of what you have circled look like *stipules* around the petiole. These are little outgrowths at the base of a leafy stem. They look like preflowers but are really just part of the vegetative phase. The preflowers will appear *very near* these stipules, though, and probably cluster around them (especially for male plants). In females, they won't be as dense as the males at first, but a VERY distinct occurance of white hairs will appear. Here are a few pictures of a female preflower and male to help differentiate between a stipule, female, and male... Hope this helps, and nice grow!

--Unfortunately, I would say the first pic looks like it may have male preflowers. There are small buds starting to form which is typical of a male in early flower. Hopefully this is only limited to the one plant if it turns out to be male....

As for your suspected burn; I would say no worries if it is very limited. It is not uncommon at all for me to see this type of burn on the leaf tips, and it usually has no effect on the grow as long as it is closely monitored and corrected (I say its best to flush when I see tip burn like that; but don't overcontrol)