I have just purchased a set of the new ultima 61mm inverted forks and was hoping someone can tell me how to check/fill them with oil and how much they take?

They should be full from the factory. I have the 58mm, they were full. The fill is on the top of the legs. What you need to do is unscrew the legs from the upper tree which usually leads to very fine scratches in the thread pattern, it's really hard not to scratch them.
My $.02, don't mess with them.

Contact Ultima Tech at (636) 931-3305 ask for Brian. Hope this helps and enjoy your new forks!!