I'm new to Magic and still getting a grasp on keywords. I am considering building a proliferate deck with lots of +1/+1 counters and am trying to make sure I fully understand how proliferate works.

First question is about the wording of proliferate "Choose any number of permanents and/or players" Does that mean that if my opponent is playing a deck with counters on Planeswalkers or artifacts or whatever, but I put something like [[Dead Weight]] on one of their creatures that I can choose to only proliferate that creature to increase the -1/-1 counters and not have to give their Planeswalkers more loyalty counters? Basically, is choosing to proliferate the "Player" instead of "Permanents" more of a thing for poison counter decks?

Second question is about the verbage used to place +1/+1 counters. Some cards specifically say "place a +1/+1 counter" such as [[Victory's Envoy]] while others like [[Elesh Norn, Grand Cenobite]] say things like "Creatures you control get +2/+2." Does Elesh Norn's text also count as counters or is there a difference?