To keep the International flavour of the boards going I'll add the perspective of an antipodean.
In South Australia I play in a competition on grass, on Saturday mornings. We play two doubles and four singles rubbers on two courts (or more it there are spares), starting at 8.30 in the morning and finishing about 12.30
So four players are needed each week, as most people like to play both (best of three sets rubbers) Or as players get older, maybe they play only singles or doubles.
A team will generally have five players, maybe six if like mine people travel for work and are injury prone.
It's very easy to organise a team!