I think this is a very exciting step for you to be taking!!
When I first started going to the gym I was terrified of the free weight area. I knew I wanted to work more with free weights vs. machines, but I was so unfamiliar with how that whole area worked. Plus, that's usually where you'll find the muscle guys, and not too many women hung out there (in the gym I started in). So I was intimidated by the guys, by the equipment, and I was sure everyone would be staring at me thinking "that girl clearly has no idea what she's doing". It was stressful enough that I dreaded stepping foot in that area.
But, little by little I got over that. It really was all in my head. Yes, I was a bit of a novelty being one of the only girls there, but honestly most of those guys really are VERY into what they themselves are doing. They are watching their biceps as they do that curl, they are trying to psych themselves up to lift a higher weight, heck THEY might be worried the other guys are judging THEM because they don't have as much weight on their bar, etc... Chances are, no one is looking at or thinking about you.
Now a days there are more women in the free weight area of the gym I go to currently. And on days there aren't, I feel like a kick *** girl strolling into that group of men and picking up some iron!
There definitely are the "regulars" at my gym, and you start to get to "know" the people that share your gym schedule. Maybe you don't chat it up, but you do the nod and smile when you see each other. I'd say that if you're anyone (fat, skinny, whatever) and you're at that gym with consistency, you get respect from the group of regulars. Gym folks respect commitment.
The only group of people I've seen gym folks as a whole be judgemental of is New Years resolutioners. Every January most gyms get packed with people who have sworn to themselves they're going to start working out. Suddenly there are lines for equipment, everything's crowded, there's no parking, etc. But most of those people don't stick around, and by the middle of Feb things are back to normal.
Just go and try to stay in your head about what you're doing. Focus on you! Let us know how it goes