It’s the standard IF Metall CBA for car mechanics. It covers things like minimum wage, minimum yearly wage increase (which is usually set to offset inflation, overtime, vacation pay and vacation time (beyond the legal minimum that is) and much, much more. You can find all IF Metalls different CBAs here but they’re all in Swedish though. The one you’d be looking for specifically is, I think, the one called “Motorbranschavtalet”.

Tesla won’t get anything different from what any other car company already has unless they specifically and succesfully negotiate a change to it. Though they don’t have to do that if they don’t want to since negotiations on changes to the CBA happen between employers organisations (which would represent Tesla as well as all the other companies who have signed the CBA) and union organisations (which represent all the unions)

I ask because others here, seemingly in favor of the idea, have stated that it doesn’t take a minimum number of employees.

It doesn’t. It wouldn’t matter if it was 1% of employees or 99%, if any number of union members working at Tesla asked the Union for help to negotiate the CBA then the Union would have to step in and try to open negotiations. And that is what has happened.