How many prints can I get out of a full set of ink cartridges? How much ink 'coverage' can I get out of a set of inks?

Depends,

Ink usage is determined by the Media Profiles and the images being printed.

Some media will accept more ink and that is reflected in the profile.
Some images have more 'color' than others.

Most RIPs allow you to estimate the cost based on the number and size of drops calculated by the RIP for each and every print.

You can find the ink cost study performed by Mutoh here:
http://www.mutoh.com/pdf/VJ12041604InkCostStudy.pdf

Coverage is another issue:

There is 100% coverage of a single color, i.e. Cyan,
There is also 100% coverage of all colors, i.e. rich black which could be 100% C + 100% M + 100% Y + 100% K = 400% ink, although most profiles will not put down this much ink.

So what is 50% coverage?
On what media?
Using what profile?

That is the reason we used standard ISO images for our ink study costs and offer only an estimation.