Thereby creating multiple catalogs can make little sense unless you have a very good reason to do so - it can make sense for example to have a "personal" one, and a "professional" one if you want to keep really separated say, your family shots from those you make for your customers - maybe you don't want to show your personal shots to a customer by mistake.
I find performance takes a major hit as catalog size increases, even if it deletes rendered previews on a scheduled basis. Therefore I don't work in my master catalog. I create a new dedicated catalog for each individual shoot or day, depending on the situation. Once I've completed my culling/processing/exporting, I open my master catalog and import the new one to it. This way I rarely have more than a thousand photos within a working catalog.
That's great .... until you try and gather images from different shoots into one space like say for example you want to find your best wedding shots to showcase to a client. Now you have to hunt around various catalogs and then re-import them all into one master one to create a central portfolio that you can edit.
Yup. Know that from experience.
4000+ images now in one catalog and no slow down. I read that it's a combo of things that slow down LR including how many of your images have been edited and how many local edits such as the adjustment brush you have applied. Liberal use of the brush slows down my laptop which is my biggest annoyance. Other than that it seems to handle several thousand images in the library fairly well.
Edit - sorry I read your post wrong and see that you first do the culling then export then re-import leaving you with just the goodies but even then I think you can eliminate a step here by simply importing all, culling and then you're done.