[PubQ] For a debut children's picturebook author, should I first try to have 3 manuscripts under my belt before querying?

I essentially have one submission-ready story, but without a background in this, I wonder if that means instant rejections. The guide on this sub says it is ideal to have 3 stories under your belt. Is it essential that I attempt to get there first? I also am an illlustrator but again, not professionally, so I know how to draw characters but not really backgrounds. I definitely can do it but I don't know if it's a smart decision for agents if I don't have the right experience with the dimensions or if it will take me a while to get the background work done. Is it smart to bring this up as a possibility on collaborating with another illustrator to draw my own characters while they draw the background, or should I just go ahead and submit it as a manuscript only?

Thank you!! This has been tough to navigate but I really appreciate this sub and hope to find further insight through this post :)