Congrats on your new addition! I only have one cat, but I have read that you should have at least one litter box per cat. So I would definitely get a second one.
I would also look for some tips on introducing them if you haven't already. My best friend added a second cat a few years into having the first, and I know she did a whole system, I believe recommended by Jackson Galaxy. I don't know the ins and outs but I know she started with having the new cat with the door closed in her own room, brought items back and forth so they could get used to each other's scent, and then graduated to "supervised visits"
before just letting both cats roam freely around the house.