Well, as I was studying some of these problems closer for one of my RPG settings, I may be able to provide some help to you.
To your first question, things that concern Angmar&The Witch-King are mostly to be found in the Appendix A to LotR, the part about Arnor and Isildur's heirs (something little also in the part about Gondor, mainly about the last battle where the WK was defeated; that is, if I remember it correctly). You can find some interesting information there (though they are just hints and the topic is not expanded), like that there are some "abandoned dwarven mines" on the North; also some things about the Lossoth etc. It's probably the best you can get about this topic, otherwise, there are hints here and there - in the Fellowship of the Ring, when the hobbits are at Tom Bombadil's or when they pass the Last Bridge, some people tell them about the wars with Angmar, but still it's nothing much. In the Unfinished Tales, in the part "Hunt for the Ring" there is something about the Witch-King and that he sent "evil spirits from Angmar and Rhudaur" to the Barrow-Downs, but still, not any precise information. I don't know if there is anything in the History of Middle-Earth, maybe someone else could tell you.
I'm afraid, as far as I know, that there are not many maps of Forochel, since largely it's presumed that there's nothing interesting in that place. Of Eriador, you probably won't find much better maps than the ones that are in LotR. Personally I use the Atlas of Middle-Earth by Karen Wynn Fonstad, which is quite reliable (mostly) and has some higher-quality maps of most of the regions. In this point, I may only warn you that it's better not to be too trustful and double-check all your sources, because people are able to imagine (or just because of poor assumptions state as credible) quite a lot of complete nonsenses.
Not sure about timeline; the one credible source that comes to my mind is the
Encyclopedia of Arda. It is still work-in-progress, but at least it's reliable, as far as I know.
Hope it helped you