BL Setup for Stock E-Maxx and Upgraded Parts Suggestions

[MountainMax]

Hi. I'm new to the forum. I've decided to go brushless. I mainly putts around parking lots and go flying around in the dirt looking for the big air. Occassional racing against the LHS employees dictate that I have some good speed too. I won't be upgrading suspension, chassis, etc unless I break something. The HV Maxx would be a decent choice for me but after reading a bit on this forum it sound like I could do better. I keep reading good things about the 9L/9920 combo so that is the direction I am leaning toward. I have some 6 cell batteries but they will get handed down to the kid once I get the IB3800 7-cell units. I like long run times. Specifically, my questions are:

Is the 9L/9920 the right setup for me? If a different setup is better, Why?
What kind of run times would I be looking at?
What upgraded drivetrain parts (like CVDs, steel gears, diferentials) do I need to get?
Would the stock gearing be sufficient? If not, what would be optimal?
Anything I overlooked asking about?

Thanks guys