For item grouping methods, do we know if there is an item limit when creating an item collection?

Not AFAIK

No issues right now. I’ve never worked with personalized catalogue views, and wanted to explore the usability of item collections.

Oh, well we have customers who have their entire catalogues defined in PCV but I don't know the details. My recommendation would be to use dynamic grouping as much as possible, but you can also create static ones just fine -- we also support CSV import if that's more your cup of tea

That’s really helpful, do you know if native PCV functionality offers any correlation of item collections to commerce categories?

Yes, you can assign an item collection to a commerce category

Does the commerce category 10,000 item limit apply in this use case? If an item collection is greater than 10,000 and is assigned to a commerce category, will all items be available?

I believe that limit is a items search API limit, so yes