Wanted to know if anyone knew which form I should start prepering for the next step...... is it the I134 or the I864???? I am not sure sure which one to prepare for Nigeria. Or do I just wait till I am contacted by the NVC???

Have you looked at your embassy's web site? Many will list the requirements.

From your timeline it looks like you are still waiting for approval.

For the K-1 an I-134 is required at the interview (some consulates do not require one but I believe Lagos does). It is best if the I-134 is dated as close to interview as possible along with all the supporting documentation that you are going to send along with it.

I would suggest reading the guides: K-1 Visa Guide

Yes I agree you should have your forms dated as close as possible to your interview date.
Lagos does use the I-134 which will have to be notarized.