We are a 7th grade team in the us doing vex for the first time, and are pretty lost on where to start. We have found a few on YouTube we want to take inspiration from, but don’t know where to go from here. thanks 
!
If you are brand new, a good start is always with the clawbot/herobots, which have free instructions online. They will give you some good references for simple mechanisms and construction practices.
That’s usually my go-to step one,
After that, its a good idea to design and build your own drivetrain, usually of a larger size than that of the clawbot/herobots, since they have a very small footprint.
In terms of other reference material, as you’ve already said, you are looking at youtube, which is good.
But a warning I give to all the new teams I coach is that the best, most complicated robots, are not the best choice for a brand new team. Try keeping expectations realistic so you don’t bite off more than you can chew.
Our league has 7-8 new teams this year (we are elementary league - grade 4-6), and we have recommended starting with the hero bot, Huey, as it teaches a lot of good build techniques and is perfectly able to play the Mix and Match game this year. If nothing else, its drivetrain is a solid performer and can be used as the basis for any number of other designs. My team of fifth graders is using a mildly modified version of the drivetrain because they felt its size, speed, and maneuverability were good for the game this year.