Q: The best audio levels for an Indie film (that will be entered into festivals)

Hi experts.

I have 553 video and audio clips ready to be edited in Final Cut Pro X and I want to make sure I am adjusting the audio properly for:

1. Dialogue

2. The loudest sound effects

3. Music

I am learning from tutorials right now and it seems the DB adjuster inside the video/audio clip may be a different number than in the audio meter? Having learning pains with this. So if i adjust the level and it hits 0 db (turning yellow or red), might the audio meter show something lower than 0? Which one do I follow?

Also, will I need to go back and change all my audio levels when I want to export separately for film festivals, dvd's, and YouTube? Or "one adjustment fits all" and the end user adjusts the volume?

Please help start me off. Thanks so much in advance.

Christine