Different ways to say "member" (of an association/group etc)

Question

I would like to ask about which is the most general/common way to say 'member' in Japanese when talking about a group, organization, association, etc. In particular, is there a word that is "always ok" to use, or does each different type of organization (a school club vs. a research society vs a sports team vs an NPO, for example) use a different term?

会員 and メンバー seem to be the most common words, is that correct? Can they be used interchangeably/in any situation?

I know about 会社員、but I'm interested more in "non company" type of organizations.

Second question: if I want to ask how many members there are in a group/association, do I just use 何名 or is there a specific counter?

Answer 1

メンバー is the safe choice that can be used in place of 団員, 社員, 部員, 班員, 所員, 組員, 会員, チーム員 and so on. 会員 refers to a member of a club/society (～会, ～学会, ～協会), and it can not refer to a member of a company, a member of a sport team, etc. If you really want a kanji word, there is a word 構成員 which does mean "member (of any organization)", but this is a very stiff word and sounds almost like a legal term.