Re: "are" or "is"?
Natives DO say the contracted "There's" all the time, before single and plural.
What we would not say is the uncontracted "there is" -- provided, of course, our speech was formed enough in out heads that we had a good sense of the rest of the sentence we were about to say.
Spontaneous speech is filled with ungrammatical utterances because the direction of what we are going to say can change a lot from beginning to end. I hardly think this is limited to English.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.