Hi
Don't know if i can be of much help as I onlygrow them outdoors. Would think the main problem would be low humidity within the house they will tolerate very low light levels..Small thread -like roots are all they ever develop ,they are epiphytes.
Have you thought of a wire basket filled with sphagnum ?? Place it through the side rather than on top.
Will be far easier to water and will help hold the humidity.. A hanging basket would allow several to be planted around the sides. Be warned !!! They do get enormous lol gary

My problem is that I don't know how to break up the rootball...

If you want to reduce or re-shape the root ball of a common Staghorn you can use a sharp knife an cut around the sides or bottom. If the root ball is soaked in tepid water it may make this process easier. I wouldn't do this in mid winter, I would wait till spring. If you are growing it indoors, good luck.