Start a pasture where greenhouses with gravel bases were?

We are getting ready to buy a house with 12 acres that used to operate a greenhouse business.  Several greenhouses have been taken out and 12 remain on the site.  Under all the greenhouses is a base of gravel that has compacted over the years and now weeds are growing there.

I want to use this land for a future pasture / animal grazing / garden.  I think the gravel should all be removed, but how?  Do I need to add fill dirt and then compost?  Has anyone done something similar?  Please any advice or recommendations would be great.

Also I am just starting our homestead and sure we are going to need a tractor of some kind.  What do you recommend, is there a certain attachment needed for this gravel removal?

Thanks!