I reccommend making life easier on yourself, and going through a process called... "Filing the serial numbers off." Forgotten Realms is a pretty standard fantasy setting. Rename all the setting specific (as in not invented by you) characters and places (search and replace is excellent for this) and then you are in free and clear legal territory. Likewise the serial numbers can be filed off of Star Trek stories. There you might want to change the physical descriptions of a few of the alien species as well. Best of luck!