For "size" I don't think you're gonna beat KY/Barkley or Cumberland Lake ... but, the Asian Carp are a problem on KY/Barkley.
For "numbers" you might want to consider Green River Lake.
And of course it depends on the weather, dates, water conditions, etc. as to the potential for your success. You might also consider "when" you plan on coming versus when major tournaments are being held on these lakes ... not only Crappie USA, but some of the Bass organizations. Not only would the lakes be crowded, but the lodging spots may be booked up.
Now, there's also Rough River Lake, Barren River Res., and Nolin Lake ... but, I'm not familiar with those lakes, so you'd have to check on the KY Forum for more info on them.