Hello, I am very glad to hear that you are taking an interest in modding.
What you are trying to achieve is much like the project I'm doing.
I would suggest using old races and heroes from an earlier warcraft series...
playing wcIII and wcII is the easiest way to get lore for your game,
and is somewhat entertaining. also before you get started I would make accouple suggestions
1# Use ArcEmu. its easier for wow modding in a couple of ways.
2# make new races that have not been in wow weather an npc or not, you will
bring a lot more to the table if the races are your own models.
3# use lore that you think players can get into. a lot of modded wow servers pull in rp players.
4# You may want to get a lore master in case your planning on expanding this wow past what your
original project will do in the future.