I really appreciate that you're making an effort to understand instead of being defensive. The one other thing I would change on the appropriateness issues is "tune her up". I know it's a very common thing to refer to guitars as female, but it could easily be perceived as sexist. (And I still don't like the name, but... that's obviously a much bigger deal to change.) Oh, I would also ditch the fake testimonials. Users don't like being lied to.
The biggest thing I would try to do is get people using at and seeing if it's useful. Presumably you know other people in real life or online who play guitar. Give them a link to one of your clips on the site and ask them to post feedback. Tell them you'll do the same for them if they post their clips.
If you can't get anyone to bite, then keep trying new ideas until you can. If you do get people to participate, try to get a sense what they like and don't like and adapt from there.
If your idea is solid and the site is useful, you should be able to grow this thing organically. Most people who play guitar know other people who play guitar. And if your site rocks, they'll talk about it, and people will find out. So focus on reaching out to the people you know and making the site rock for your group of guitar-playing friends (while still being inclusive of everybody).
Then, once you know it's useful because you've tested it within your group, reach out to other guitar communities on the internet.