Kamahl’s last ability affects only creatures you control as it resolves. Creatures that come under your control after that point (including lands that become creatures) won’t get the bonuses.

Lands that become creatures retain any other supertypes, card types, subtypes, and abilities they have.

A noncreature permanent that becomes a creature can attack and its abilities can be activated only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature. Notably, if you turn a land into a creature on the turn it entered the battlefield, you won’t be able to tap it for mana.