My brother asked me to make 16 cakes for my nephews 16th bday. I haven't said yes because I wasn't sure if I was going to be able to take on such a task. He didn't exactly say mini cakes but looks more like maybe 4-6 inch individual cakes.

How far ahead can I bake, fill, frost, and cover in fondant? Since they'll be so many I'm worried I wont have any time.

You can bake at any time and freeze the cakes till you're ready to fill, crumbcoat and cover them. And you can start putting them together at least a week in advance with no problem (unless you're planning on using a filling that needs refrigeration, but you might not want to do that anyway on a project like this). A week of wiggle room - you may not actually need that much - should give you plenty of time to get everything done. Maybe it would help you psychologically to think of them as "big ole cupcakes" - that's the way I would approach it, anyway. Hope that helps a little!