Cliche, I've got to tell you, I've been in your shoes.
I'm still a newbie, and I'm not interested specifically in salsa, but in ballroom, latin and swing in general. I've had a few intro salsa classes, and have danced some salsa socially, but it doesn't really matter.
I was terrified to start taking lessons, especially group lessons. I've always been a wallflower. (Literally, when I was little, there were times when the idea of having to speak and interact with other kids--even ones who were making an effort to be nice--would reduce me to tears. I'm not kidding.) I'm much more outgoing now, relatively, but the idea of showing up to group lessons, without a partner, when I'm far from drop-dead gorgeous, and clumsy on top of everything... Wow. I was terrified.
And I put off starting to take lessons with one excuse after another for years. And then once I finally got up the courage to go and watch a lesson I saw that everyone was really, really, really nice to me and made me feel welcome. And that there were people who weren't "all that" who were dancing and having fun and no one was turned off by how they looked. Everyone was just having fun trying to learn the steps and (occasionally) laughing at themselves in the process.
All I can say is, I wasted years being afraid. I kick myself every time I think about that. But then I stop and think of how happy I am that I finally tried it. It's been the absolute hardest think I've ever done in my life. Without question. But also one of the most rewarding. And I've met so many new friends and acquaintances. An no one cares how I look, or that I'm not as skinny as I could be, or what have you.
As for the partnering question...like I said, I showed up without a partner. I've always showed up alone. It's hard, I'm not going to kid you. But it gets easier, and you get to know people, and then it doesn't matter as much. I can see that in a while, it won't really matter to me at all. For group classes, my teachers usually line up men on one side, and women on the other. You partner with the person across from you. You practice with that person a bit, then we "Rotate!" and (usually) the men move down one lady. And then you practice with the next person. If you don't have a partner because there are more ladies than men, you practice by yourself for a bit.
One of my teachers (the lady) sometimes stands in as a lead, so I've ended up dancing with another woman. No big deal...I'm too busy concentrating on what I'm doing to care. I've seen my teacher ask a more experience gentleman to lead him (teacher dancing as a follow) when his partner wan't handy. It's not a big deal, and it's never even addressed as something out of the ordinary. But, I've never seen 2 male students partner each other.
I hope this helps. Just go. Maybe youwon't like it, but you don't know until and unless you try. If it's a good studio and a good teacher, they will help to make you feel welcome. Good luck!
--Peaches