Welcome.

I always ride with husband. So never is huge crowds.

But I did for the few outings we did that had 4000++ cyclists or one of 1000+.

I had no issue but I kept my distance from others. I'm a good stable rider (at least this is what hubby says) so it did not worry me. You'll have to remember that not all cyclists leave at once. They generally leave by "speed" group, at least here. If you're fastest or slowest, you may be starting first group or last. So most of the other riders are already gone by the time you leave, or you have a headstart on them and they will pass you by the left (the norm anyway).

Just enjoy the ride! No reason to embarrass yourself. Worst you can do is not finished and cry (like I did). But when you do (which I did too), the feeling is awesome.