Just a quickie… FCP X 10.1.3 works fine in Yosemite. Snappy even! No problems yet , and I’ve been hammering it for a while. Go for it!
Also, for what it’s worth… FCP 7, Adobe Pr and AE CC, Soundtrack Pro all good as well. No functionality differences from Mavericks as far as I can tell. Avid MC 8 appears to be OK, though I haven’t done much in it, and Resolve 11 seems OK too, though I had to switch the GPU to use OpenCL rather than CUDA. Might just be me though.
So… All good, dive in!. But, if it all blows up… don’t blame me!