How many items can you sell before you should pay vendor fees?

Yep. Just scroll on by!

Exactly. Not hard to do.

I thought if you hit the "ignore" button for those users that post and annoy you, problem solved. Correct?

That's also true. If you're not looking for any parts that would work. And if those sellers comment in another thread you get a "show ignored content" message so you really don't have to miss out on anything useful they may post in a thread you're looking at.