Complex Expressions, Commas, and Conjunctions

Some places online have said sentences can begin with conjunctions. Also, are there there some places where commas are absolutely needed? Finally, should complex expressions be a negative thing for ratings?

Finally, some people are ending questions with periods, and some words like built-in are sometimes spelled without a comma. You would have to know which words fit that category.

Complex expressions seem to be a matter of taste and shouldn't be a big deal.