Granny Square Blanket Question! Can Someone Answer?

I am making a crocheted granny square blanket seeing that it is getting to be cold out and I have a few quesitions. How many squares do I need to crochet of each color to make a blanket for an adult? and...Can I do them all seperatly and then put them all together or do I have to connect them all at once? I appreciate anyone that can answer. Thanks alot!