Adding this new toilet so that it meets the code and works flawlessly for years requires a moderate amount of skill. Many cities and villages allow you to do the work so long as it passes a rough-in and a final inspection. My advice to you is to try to do the job. You can always call for the cavalry if you get overrun.

This new toilet will require a 3-inch waste drainage pipe. You may decide that plastic PVC is easier to work with, but if I was working with you and it was important that the pipe was quiet, we would use cast iron pipe.

The two biggest challenges with the drainage pipe are connecting it to the existing drain line and then properly venting the new toilet. If you can successfully cut into your existing drain line and install the required 4 x 3 wye fitting, you have what it takes to complete the job.

In case you do get into trouble, a plumber is the primary contractor you will need to bail you out. This assumes that you can do all of the drywall repairs that will be required after the vent pipe is installed.