when done with tape and mud, you must prime.

thanks for the quick reply! can you reccomend a type of primer? also is one coat sufficient?

I usually go with Behr from HD, although almost any primer you can get from HD/Lowes will do the job. 1 coat is sufficient

If you use latex primer, you will have to lightly sand it afterwards, as it lends to raise the grain of the drywall. Be sure to clean off the plaster carefully after you are done sanding, as the dust will show in your finished job.

Oil based primer does not raise the grain of the drywall, but it is obviously a lot more bother.

Use latex PVA primer, thats what it's for.