Bathroom wiring has a bunch of specific code requirements that add up fast. You need at minimum: one 20A circuit dedicated to bathroom receptacles (210.11(C)(3)), GFCI protection on all receptacles (210.8(A)(1)), a switched lighting circuit, and ventilation either by exhaust fan or window per IRC M1505.
The 20A bathroom receptacle circuit can serve multiple bathrooms but cannot serve any other outlets or loads. A lot of old houses have the bathroom on a shared 15A circuit, which is a code violation in current NEC. Anytime you pull a permit touching a bathroom, know whether you’ll be required to bring it up to current code.
Exhaust fan wiring: 120V, typically fed from the lighting circuit with a switch or from the 20A bathroom circuit. Combination light/fan/heater units need to check their amperage draw - some of the heater combos draw 12-15A by themselves and need their own circuit. Read the nameplate before you wire it.