You can currently add up to 50,000 songs to your collection.
It's also worth noting that only songs in the Music folder on One Drive are added to the collection.
If you have an Xbox 360 or a Windows Mobile phone, then your best bet on syncing all your music and media would be Windows Media Player 12.
Sadly enough, you may have already encountered problems refreshing your library and keeping things tidy.
Even if this workaround was effective, it seems pretty micky mouse considering that you have to manually remove all files, which could be comprehensive, then add them back in again to result in failure anyways.
In much the same way you can with some competing music services, Microsoft's Groove will let you play your own music from the cloud.
And if there is an issue, there are so many easy to find and apply solutions online.
So instead of finding something else right away and researching it. This seems to be the theme for a lot of MSFT titles. WMP is a big effort on their part and since I'd rather not have to fix it so often I use other titles.
It is a real pain to get media player to update the library.
It eventually will but I can find no rhyme or reason as to when it will do it.