I like the video, it's pretty great for those new to the game. Good work!
I'd like to say something about your first point: In KF1 they made it such that a mass of zeds would spawn on isolated players in order to pick them off. It may be worth looking into whether or not that's been carried over to KF2, and mentioning it in the video.
As for point four on your video, I'd say be careful about bagging on the medic role too much; if I were a new player to the game, you would have put me off of wanting to be the medic, despite its necessity. I think it would suffice to say "it's a high pressure role", and maybe expand more on some of the plusses of being a medic.
For example, although they don't get damage increases with level their guns are still very relevant (until HoE) due to their high base damage. Plus you get cash from healing people. Stuff like that.
Finally, some other points you may want to consider adding: Weaknesses and resistances. FP's take bonus damage from explosives, scrakes take less (i think half) damage from grenades.