You should have a skill on your bar by now that will reveal all of the contents of the high level nodes. It is best to wait for your new gear to sprint bond with you before you try to meld it or some of the melds may fail and that is very expensive if you are using IV materia which you will have to get more than the 0 chance for the high items. There are a number of threads about the best melds and way to gear up but it is expensive and not easy to do. Good luck.

as for the locations, there are excellent lists around but i hate to post them here to spoil others. Keep looking.