Hi, I'm not sure I completely understand your first question. If you mean is it OK to pick out e.g. Hazel leaves amongst several Oak leaves fallen in the same place, then yes that's OK, as long as you're happy with the ID. Also I would make sure there are no bird droppings on the leaves, as bird droppings can contain viruses.
Yes, it's perfectly OK to post lots of plant pictures for identification, either here in your own thread or in the thread called A Foraging Diary. We'll try to do our best to help. Ideally, the pictures should be of the whole plant, an individual leaf and a flower (if it's in flower).
Foraging is great fun!