Anchor question from a newbie

Will a 7lb grappling anchor work for my 13 1/2 foot aluminum boat? Or should it be heavier? I'll be fishing mostly in lakes but might take it into the bay to do some crabbing. I'm not sure what kind of bottom the lakes will be. I'm guessing mud and maybe some rocks. I'm in New Jersey. Also, I've read that I should have a chain between the anchor and the rope. If so, how long? Should I have 2 anchors off opposite ends of the boat to stop from spinning?

By the way, thanks to everyone who commented on my other posts and answered my questons. You've all been a great help.

basspro has some suggested weights for different size boats and types of bottoms, etc, most descriptions of the anchor will tell what type of bottom they will work on. I dont use any chain on mine but I'm inland so no saltwater experience, and use 8lbr's mushroom on my mud bottom lake on my tracker pt175. Two anchors will stop the spinning from the breeze & currents.

Attach a 3' heavy chain and you will be great with that anchor