Fabric - rows per table limitation

"Is it correct that direct lake rows per table limitation means that I can exceed the limit but that it then will use DirectQuery? Is it the same for lakehouse and warehouse?"

"Are there any limitations on semantic model size?"

Yes, see the answer from AndyDDC

"what is the suggested method to list numer of rows and size per table in lakehouse/warehouse?"

"What is Direct Lake mode size?"

Many tools can count the rows in the table. The most common approach is probably to use notebook or SQL endpoint to do this.

Regarding how to calculate model size, check out the "Memory footprint" section of this blog post:

https://data-mozart.com/50-shades-of-direct-lake-everything-you-need-to-know-about-the-new-power-bi-storage-mode/

Also check out this blog post, I think you can calculate the direct lake semantic model size in a Notebook: 

https://fabric.guru/calculating-and-reducing-power-bi-dataset-size-using-semantic-link

I think the size of a direct lake semantic model depends on how many columns are cached into Power BI Memory. So I think the size of a direct lake semantic model will depend on which columns are being used ("warm", i.e. loaded into the Power BI service's (Fabric's) vertipaq engine's memory).