How many shells does a typical tank have?

Yes, tanks need constant refueling, rearming. Tanks generally carry two types of shells for the main gun: AP and HE.

British challenger mk2 carries 52 rounds of 120mm ammo for its main gun.

An M1 carries about 40 120mm or 55 105mm rounds depending on how it’s configured.

This is the sort of question that startles me. If I were to ask “How many occupants does the typical car have?”, I wonder what the reaction would be here.

There were several models of Sherman tank with different types of cannon and different ammunition capacity, ranging from about 70 to 100 main gun rounds (generally a mix of types). Yes tanks did/do need to be regularly resupplied, especially with fuel. Also, maintained and repaired.