I've had my 8 girls since August, and picked up loads of dos and don'ts from reading this site, and asking daft questions, and joining threads etc. Also read every book I could lay my hands on, and visited as many chicken keepers as I could. It's good to see other people's set up's and learn from other's mistakes.
Not sure about a dog kennel. Would depend on size etc. People on here have modified all sorts of structures, so it might be possible to convert it for chucks. I used 2" x 1" timber planned with rounded edges for our perch. Chickens have surprisingly big feet, and a broom pole wouldn't be wide enough for comfort. So . . . don't believe everything a breeder tells you!
Perch is about 18 inches above floor level, but I've a big coop, and they still have plenty of head room. Outside in the run they have a variety of branches for perching, and also like to 'tight rope' walk along the top of the compost bays! Very nerve racking to watch!
Hens seem to like a bit of privacy for egg laying (a bit like us using the toilet), so within the darkest part of the coop (but with easy access for eggs) build or provide a smaller enclosure with soft bedding, eg straw (not hay), and that should be OK. Need one nest box per 3 hens I believe. Our 8 share 3 nest boxes.
Re pen, make sure it's as fox proof as possible. 6' x 6' a bit small for 3 hens? Depends on how much time they will be in there. Can you put the kennel on tall legs to give them maximum floor space in pen? Would also give them a bit of shelter from rain, and somewhere dry to hang feeders.
During day light hours they will need constant access to layers pellets and clean water, and if possible in the afternoon a small treat, eg corn, or veg etc. Also need access to grit (for digestion) and fine oyster shell (for calcium).
Don't need any food/water once they've roosted. And personally would recommend that food containers are removed every night to prevent rats.
Don't know anything about ducks, but lots on here do.
Best of luck. Keep asking questions, and post pics asap.