If you are interested in tech speaking I will be happy to share my journey how I started, Ask Me Anything!

Here is my combined answer -
I am following this approach Crawl -> Walk -> Run. So using this approach I follow this route Meetups-> CodeCamps -> RegionalConference -> NationalConference -> InternationalConf.

So here the audience does not matter for the above approach, as it depends on people's interest, if they are interested to hear your topic which you are going to convey. If it is something new you are going to speak you will see more audience. If it is something old concept but you are an expert in that, people will still like to hear it from you. There are days where I traveled to a code camp where I had 2 people attending my talk in afternoon and full room in the morning. Even experienced speakers face situations where they will be left with less number of audience. So number of audience should not be a driving factor if you are starting.
Knowledge on a subject is more important than number of years of speaking according to me. If you have a fresh perspective which you can share then number of years of speaking does not matter. In tech space every concept changes every year, having the knowledge is more important and the passion to share the knowledge with developer community is more important. We need not be an expert on the subject if you are introducing a concept to newbies, but you should know the ABC's to clear the doubts which newbies might ask. So knowledge level depends on the audience mix and whom you are targeting like beginner, intermediate, advanced. Yes these levels increase the knowledge on the subject should increase.
Hope I have answered your question.