Advanced IMovi Questions, and a podcast please?

Hello all:
I start using Imovi, and I found some youtube Tutorials for that, but the most important and professional 1 is By Blindie Chicks, you can find at:
https://youtu.be/gInthWUriLM
I found more tutorials, and i finish all of them i think, but still i have some questions if anyone can help me:
1- how can i put a video between 2 videos?
2- How can i adjust my Video sound if it has problems?
3- If i have a music track that i need to sync on my Video, is it accessible?
4- the IMovi Export a very large video size, is there a way to make it smaller?
Sorry for all my questions, or if you point me to a good series of podcasts that explain the Imovi in details.
thanks in advance