The conjunction そして is used at the beginning of a sentence to add more information to the one given in the preceding sentence. Here, it is used to connect two adjective sentences.
あの へやは ちいさいです。そして、くらいです。
That room is small. It is dark, too.
Lesson 1-1「マリアさんと ローラさん」
Maria and Laura
と as in Ｎ1 と Ｎ2(Ｎ1 and Ｎ2) is sandwiched between two nouns and cannot be used to combine sentences. Thus あの へやは ちいさい です。と、くらいです is ungrammatical.