Suppose that $B$ is a complete Boolean algebra and let $S$ be a countably infinite subset of $B$. Let $C$ be the smallest complete Boolean subalgebra of $B$ that contains $S$. Is $C$ isomorphic to $\wp(\mathbb{N})$, the power set of natural numbers?
I think that the answer should be positive as $S$ generates a countable Boolean algebra on its own, so it embeds into $\wp(\mathbb{N})$. Taking completion should be in a sense coherent between $\wp(\mathbb{N})$ and $C$ but it may well be wishful thinking.
This is quite false, as demonstrated by the following theorem of Solovay.
(This theorem can be found in S. Koppelberg's Handbook of Boolean Algebras, vol.1 (J.D. Monk, ed.), p.191.)
So there is no bound on the cardinality of a complete Boolean algebra with a countable set of complete generators.