Is there a hard limit on the number of blocks that an EPiServer page can hold?
2 instances includes
1- Block with parent child hierarchy(Carousal block & Carousal Item block) - This includes 100+ Carousal Blocks on a single page.
2- Block with a single parent (Carousal block)and multiple child(Carousal Item block)-1 Carousal Block with 100+ Carousal Item blocks
I don't believe there is a hard limit within a CMS for the number of content items within a content area.
I would however suggest that this is a red flag for performance as each content item used is a content item to load from the database/cache and to be verified as accessible by the user, I'd definitely recommend the use of Content Output Caching here. It will also mean that you're likely adding a large number of elements to your DOM which will result in a reduced performance score in Lighthouse and potentially negatively affecting the SEO impact of the page in question.