Preschool party etiquette

Preschool party etiquette

My son has been invited to his first party. Well, not really his FIRST birthday party, but the first where the rest of the family isn't invited. A classmate from his preschool class is celebrating his bday this weekend at their home. We got the invitation in the mail over the weekend and he's really excited about it.
What makes this invitation blog-worthy? Well, I feel it's a milestone of sorts. And I'm in a bit of a quandry.

1. We've been to countless bday parties but we've always gone as a family. They were bday parties of children of our friends. This is the first time DS is invited and we don't know the parents aside from nodding a polite hello when we drop off the kids and pick them up from school.

2. Since only DS is invited, do I just drop him off at the house and pick him up when it ends? Or does an adult accompany him? Is he too young to be left there? He is after all barely 5 years old. On the other hand, I don't want to stay or impose on the hosts by staying when I am not supposed to stay. What is preschool party etiquette?!?

3. Is it okay to ask the host if an adult should stay with DS? Or would that oblige the mom to ask me to stay? Again, I would really prefer not to go with DS because then I would not have to get a sitter to watch the other 2 kids.

4. Ok, if I just drop off and then pick up DS, is he going to be fine? This will be a new situation for him. I'm pretty sure he'll do just fine but the mommy in me has a tinge of worry, you know what I mean?

We're navigating unexplored areas here. I did not grow up in this culture so I am not really sure how things work. Please somebody help me out here...

Then again, am I blowing this way out of proportion? I have a tendency to overthink stuff. What do you think I should do?