1) Is there some sort of adapter or splitter that I can get so that I can input to both ports and record stereo tracks through my microphone?
** Can you elaborate a bit as to why you'd like to record your vocals in stereo? Most of the time, vocals are just tracked in mono. After you've tracked it, you can then duplicate the recording in Studio One and then move your duplicate to a second track. If you're thinking something like "I want to put my one microphone over my drums and record in stereo so that I can pan the hi-hats to the left and the floor tom to the right", you won't be able to do that with one microphone. You'd want to get a second microphone and utilize the second input on your interface.
2) Is there some kind of adapter or splitter that can split the output from the headphone jack to two separate sets of headphones?
** Yeah, any 1/4" TRS to Dual 1/4" TRS Dual splitter ought to get the job done. Keep in mind, this won't give you two separate headphones mixes - you're each going to hear the same thing in your headphones.