I can't speak to your actual question regarding attracting bears and coons to the feeder, although I wouldn't expect that to be an issue. The main benefits of this feeder are keeping out rain, mice, rats, and wild birds. It does an amazing job at this!
Unfortunately I can tell you from experience that the Standard Grandpa's Feeder isn't likely to work for your squirrel problem! I have learned this the hard way and I would love to hear if anyone has a good solution to the problem! I think the Large size one would work, even though it sounds like overkill for the size of your flock.
I have one of the Standard Grandpa's Feeders and while I really like it, it does NOT keep squirrels out...maybe it will work for chipmunks--the issue is the weight of the thief! The treadle is designed to operate on a weight of 500gms. The Large Grandpas Feeder requires 900gms to open--maybe this will do the trick. The problem is that squirrels average 500gms (and the fatter they get, the easier time they have!), so they have no problems opening the treadle and stealing to their hearts' content.
My girls free range daily with their run and coop open; I keep the feeder in their run and the squirrels have discovered how to go through the coop to the run and open the feeder...the only solution I have found so far is feeding the squirrels at their own station on the other side of the property! Boo! Any suggestions are certainly welcome

I found the folks at Grandpa's Feeder to be very helpful and responsive when I had a question previously, so I have been meaning to see if they have any input, but keep forgetting to ask them during business hours! You could ask them about your situation too
Good luck Specialk!