To answer a few things:
1) The first video will focus first on base, just because base will be the easiest way to get the concept of the game across: trying to focus first on LT will just make people think "besides the jetpack and large landscapes, why do I want to play this?"
Most games coming out nowadays are rife with weapons, classes, lots of customization and so forth.
This leads into #2:
2) I am definitely going to cover all of the major mods: I could probably cover all of the weapons, armor, deployables, packs, grenade/beacon/mine differences for a given mod within 5 or so minutes.
A lot of my viewers are very high-stimulus people, meaning they've been playing games for years that send barrages of stimulus and input to their faces/hands/feet, so blowing through all of that in 5 minutes will be more than enough time for them to understand. That, and there's always the pause button.
3) That said, i'm also going to cover LT just as much as I will any of the other mods, but since there won't be much to cover as far as weapons and armors and all that goes, this is where i'd probably use the pro clips from, and try to give off the angle that LT is the "pro players" mod, where crazy shit like mid-air flag passing goes on. This will ensure that the LT players will get (probably) mostly experienced FPS players and people who are into high levels of difficulty, whereas the less skilled players will probably start on base or one of the mods.
4) A lot of my viewerbase, as well as just gamers in general nowadays love customization, lots of options and so on. This is another reason i'm going to feature mods, but i'm not going to give any one mod more air-time than another.
Percentage-wise, the three or so videos i'm going to do will probably look like this:
40% = Base
50% = Mods (including LT)
10% = Advanced techniques, clips of pro players doing ridiculous stuff, either in it's own video or intersected within other videos
People learn best when there is an identifiable "core" to base their learning off of, and in this case the reason i'm featuring base so significantly is because once i've put it into their heads how all of the main features of the game work, like generators, inventory, deployables, etc. then understanding the other game types will come much easier.
I know LT is an exception to this, but again I plan to handle that differently than the other mods, as noted above.
Finally, as far as making it known that teamwork and such is a big deal, i'll try to do that for sure: I remember when Tribes 1 first came out and people were really acting as a team even on pub servers, and i'll definitely point out that there are given "roles" within most teams, such as:
-Building defense
-Repairing defense
-Destroying enemy defense (offense)
-Flag cappers/carriers
-Snipers (only on some maps)
-Building remote bases (complete with defense, all of that)
and so on. I'd also go into sub-roles, like how you could destroy their offense blatantly with a Heavy (or in mods, whatever heavy armors there are), or use a weaker, cloaked/sensor jammed/chameleon armor and take out defense covertly, planting mines along the way, so on.
Hope that answered a lot of the questions, right now i've got two huge college assignments going on as well as my own projects i'm working on, music videos etc. but i'll try to get to this as soon as possible, I should be able to start work on it definitely before October ends.