Get as much as you can safely afford. You won't regret it. I'm personally a Humminbird user and would recommend you get a side imaging unit. If you can't afford them, then you need to decide if you want color or black/white. Personally, I never thought color was needed unless you're going to use detailed mapping cards. Black/white will even look better in the sun.

Check these out.

Humminbird Lake Fishing