Only having one switch to power more than one fixture is never a problem as long as you do not exceed the amperage for which the switch is rated. A standard single pole switch is rated for 15 amps; you would have to use the equivalent of 12, 150-watt light bulbs to reach that rating. Hooking up a bathroom fan and light on the same switch is actually a more convenient way to wire two fixtures than adding a separate switch. If you want the fan and light to turn on at the same time, it's an uncomplicated process.
Turn off the electrical power to the switch by turning off the breaker in the main electrical panel.
Locate the black power supply wire in the electrical switch box. The power supply wire connects back to the breaker panel.
Locate the black wires from the bathroom fan and the light. Both of these wires connect directly back to the fixtures.
Cut one 6-inch piece of 14-gauge, THHN, solid-black wire using the wire cutter/strippers. Use the same tool and strip ½ inch of insulation off both ends of the wire. This is your pigtail.
Connect the two fixture wires to the pigtail by twisting an orange wire nut onto all three wires.
Connect the pigtail wire to the switch. Twist the pigtail around the top screw on the right side of the wire and tighten the screw.
Connect the power supply wire to the switch. Twist the black power supply wire around the bottom screw on the right side of the switch and tighten the screw.
Attach the switch to the electrical box. It attaches to the box at the top and the bottom of the switch with the screws furnished with the switch. Cover the switch and the electrical wiring with a switch cover plate by attaching it to the wall with the screws provided.
Turn on the electric to the switch by turning on the breaker in the main electrical panel.
Always ensure the electricity is off to the area that you are working in to avoid electric shock.