I’d put the map room at a place where you visit often. If you have a single base, then that’s the smartest place for a map room, since that’s where you’ll be visiting most of the time. Of course, if you have someone else’s map room at your disposal within a convenient distance, having your own there would be redundant.
So from that point of view, and since your base is close to an obelisk, it might make sense to build your map room near another obelisk you visit often. That way, you can teleport between the two easily.
And remember, map rooms can be picked up, so even if you decide your chosen spot wasn’t ideal, you can move it elsewhere when you feel like it. Just remember to build a big enough secondary base that the decay doesn’t catch your map room by surprise.
Unfortunately (well, unfortunately for you, fortunately for me) I managed to collect so much demon blood before they reduced its drop rate that I haven’t paid attention to what drops it and how much - I still have chests full of the stuff in several bases of my own. I’d try something that spawns 100 % (such as a Rocknose king), but wandering the shores of Noob River for corrupted shalebacks might work too. At least both of these are easy to kill. Then again, your base isn’t far from the Unnamed city and the Red Mama…