The difference is that a sub-committee is set up by a committee. They are rare in small councils, since committees appointed by the council are usually sufficient. Committees are not often given the power to create subcommittees when they are set up by the council. Committees and sub-committees are all open to the public unless specifically excluded by resolution, giving reasons (in outlilne). Committees normally report to the council. Non-councillors can be appointed to any committee except a finance committee, but only in limited cases do they have a vote.
Anyone at all can take minutes, but they must be approved. Normally committees approve their own minutes and they are noted by the council. It is up to the council to decide what meetings to ask the clerk to attend.
By and large, it is best for reports to be presented in writing and not verbatim. Reports should be made available to councillors and public along with the agenda. It clearly saves time to avoid verbatim reports, while not precluding discussion where appropriate.
Normal council business should not, ideally, be handled by working groups for obvious democratic reasons. Working groups are best for exploring complex issues and bringing them to a point where specific questions can be put to the council or a council committee.