OK, I'll bite. What are these primary sources? I've got hardback of Weinberg's Principals and Applications and of course MTW's Gravitation (a self demonstrating object), but I'd really recommend Caroll's Introduction for the coverage of cosmology.

Get into the notation and tensor formalism of raising and lowering operators, etc. It really helped make some of the results more clear to me, just as <bra/ket> helped with QM.

Or are you doing high end astronomy or building a back yard Wave detector? That would get truly expensive!