Is every language with a finite number of strings regular?
Yes. Assume the language is $L=\{w_1,w_2,\ldots, w_n\}$. then you can form the regular  expression $w_1 + w_2 + \cdots + w_n$, which describes $L$.
You can also argue with finite automata or regular grammars.

Yes, if your alphabet is $\Sigma=(a_1,\ldots,a_k)$ then the regular expression $(a_1+a_2+\cdots +a_k)^*$ describes the languages of all possible strings over $\Sigma$.