I'll try and give you a couple of ideas,I kept goats for years,despise sheep,but was surrounded by sheep farmers ,a couple of which paid me to help out on their holdings,so I've a fair bit of experience with them,shearing,'tagging' and especially lambing.
Although it's not cast in stone,for me(and many will disagree here) both animals have different requirements.Although many goats are kept outside on grass.where a sheep would thrive,in my opinion goats do better on a, predominantly ,hard standing.In this way they avoid the dreaded foot rot,and you don't spend so long manicuring.
It may be conceivable ,in a large enough barn,that both animals could knock about together(sheep are herd animals,but Large males/wethers do seem to be OK outside of herds)but they would all need a bit of space, it MIGHT work.
What's wrong with keeping the milk goats and eating the inevitable billy kid?? Go on,close your eyes and pretend it's mutton...................tastes better anyway!! BWs.