If you plan on keeping it in a container, I would prune to keep it nicely shaped and manageable to move in or outdoors.
I have grown three container grapefruit trees. When they become too large, I would trim both the foliage and the rootball to keep it in a container which I could manhandle. I'm sure you've noticed the citrus odor if you crush a leaf.
Grapefruit don't come back true when started by seed. They are grafted. Mine never bloomed or fruited. But the leaves are enjoyed by the caterpillars which become the Swallowtail butterflies so are fun to grow for them.
Hope you enjoy your pretty plant.
And just a suggestion, I took a nail clipper and nipped the thorns off. They can be wicked...
