In WCS7, is there any limitation to the bumber of itembeans associated to a Product bean
There is no hard limit in how many items (SKUs) you can have for each product, but you should consider the performance implications, both for listing on the product page, but also the size of your attribute tables.
I would challenge that if you have this need, there may be better approaches, e.g. if you're trying to model an ability to customize a product (e.g. "I want 20cm of this fabric"), you can use the product attribute model (see the PATTRIBUTE table) to allow shoppers to add custom attributes to the product when they add to cart.
The Extending an SOI service with UserData tutorial in the V7 Knowledge Center shows an example of doing so through engraving attributes for a product.