Single pole switch 3speed fan control and light control(dimmer) I have a 12/2wire from panal and a14/3 to thd fan. Is this all I need?

What is the amp rating on the breaker? If it is 20 AMP, you need a 12/3 to the fan. If it is a 15 AMP, 14/3 is OK. Can't mix AWG unless you go to the lowest rated Amperage. For example, you can run a 15 AMP on 12 AWG but not 20AMP on a 14AWG

Are you adding the switches to the circuit or have they been there all along?

Fans usually are fine on a 15 amp circuit, however, you may have a different problem.

If your home was wired with Aluminum wiring (older homes) then you have to make sure the connections to the new copper cable are made correctly. If your home already has copper cabling, then you are fine.

Next problem, Do either of the new switches require a "Neutral Conductor"? If so then the wiring is a little more complicated.

Using #12 AWG conductors for the switches is fine as long as you do not increase the amperage of the circuit.

If Neutral is not required at the switches I would use a 12/3, however, if Neutral is required then I would use 12/4.