I'm little confused about rules.

It is said:

"If the active player has a base on the active planet, he can build a number of units equal to his unit build limit ."

Does it mean strictly equal? F.e. if my unit limit is 2, can I build 1 unit?

Of course you can build less than limit, just like you don't have to build everything what Build order allows to. All up to your choice.