Writing/Pitching PB series

One of the ideas I'm working on is a humorous picture book series inspired by my dog (who serves as the mc). The tone and format are very similar to Mo Willems' pigeon books.

I've completed two manuscripts and am working on the third right now. Before I go any further with this idea, I want to step back and clarify a few things:

1) From what I have read, some agents/publishers like being presented with series ideas (obviously potentially more lucrative), while others may turn away from it. Can anyone expand on the pros/cons from their perspective?

2) If you have a series in mind, do you mention it in your query letter for the first of the series? If so, do you need to indicate how many you anticipate in the series or is it ok to leave that open-ended?

3) How many of the series ms's should you ideally have complete before querying? (If you say it's the first in a series, I'm assuming it's likely an agent might request to see everything else you have done in that series - so would, say, 3 ms's be respectable?)

thanks!

Thanks Brandi. I remember reading somewhere that it was a bad idea to mention a series in a query (can't remember where), but then I saw some advice to the contrary in my google searches. BUT the ones who said to mention the series were for adult fantasy/sci-fi books, not PBs so I don't know if that makes a difference or not.

But yes I agree that any single piece should stand on its own merits...I believe it does, but I have a habit of always getting ahead of myself

Thank you, JudScotKev. That makes sense.