I'm no expert but since I'm in southern WI I'll throw out what I've learned owning a pond for the last year. As far as depth yes you can slope your beach area 4-1 then have it drop faster further out. The main reason for gentle slope is safety for kids and it helps the sand from washing down the slope so fast as will some retaining wall at the edge of the sand (under water and deep enough that no one will dive into it) and underlayment like a geo textile fabric between the sand and dirt. The problem you'll have is its easier to do that while the pond is empty and if it fills that fast you'll have to run a trash pump while constructing to keep it dry. If you have a more steep slope other places than the beach that helps with weed control, mine are very steep to about 10 ft and I have little to no weeds in my pond. Do a google search for "building a beach pond boss" and you'll see several threads on beach building. If you have electricity with in a few hundred feet I would get a bottom diffuser and pump as this helps with water quality and prevents muck build up on the bottom from organic material. I'm running mine 24-7 365 to get ours in better shape before we venture in for a swim, it's had nothing done to it in 40 years so I'm rehabbing it into what we want. For size and depth I would go as big and as deep as you can, i don't think anyone ever thinks their pond is too big and the deeper it is the better any fish you put in will do over our winters! I would consider using pond dye from the start to cut down on weed growth and it gives the water a nice blue look for swimming. For fish I would go with yellow perch and smallmouth bass as well as fat head minnows. Yellow perch are great at controlling leaches, snails, ect and the bass keep the perch in check. Stocking permits are easy and free to get from the dnr and you'll need one to buy from a fish farm. Good luck with the project! I never knew how much fun (and work) a pond was until we owned one and now the kids and I have a blast tinkering with it. My son caught his first fish out of ours tonight, it was only a 6" bluegill but that's one that both of us will remember forever!