Generally ok - I think your original menu sounded great and I can and will happily give you a few ideas for a one pot dish, I think it's not as 'summery' as your original idea.
So, here's how to do a really easy potato dish.
Peel some ' old' potatoes, like white, red skin, Maris piper, Desiree.
Cut them into slices. The easiest way to do this is to cur a slice from the long side of a potato then use that flat side as the bottom so the potato does nit move while you slice it. Slice it into thinishh slices, about 2-4 mm thick. Put these slices in a bowl of cold water and leave them for an hour. So, after an hour or so drain the pots and rinse them. Get a good sized non metallic dish and rub some butter round it and a bit of garlic. I buy garlic paste from tesco ( Gia garlic paste, from Italy) and I rub a couple of cm round the dish. If you use fresh garlic just cut a Clove in half and rub it round the dish. Now start layering your potties. Remember, the only ones anyone will see are the ones in the top so you don't need to be prescise. I just throw a third of the pots in, and season them well. Use more salt and pepper ( white pepper if you have it, but black is fine) than you would think. Dab a teaspoon ful of butter over the pots. Do the next layers he same and the next and keep a nice potato,or two for the top. This is where you put them in lines if you want it to look cheffy. I often just throw those on two- I like rustic! Now, this is where you decide if you want potatoes that taste divine but have about fifty hundred calories per mouthful. If you do, mix a pot ( I'm being ambiguous with quantities and I'm unsure how many you are cooking for. It's it's 4 I would use a 300ml pit, if it's 6 plus I would use a 600ml pot) of double cream with a small amount of milk to ' slacken it' now pour the cream all over the potatoes, gently shaking the dish to make sure cream goes in all the gaps. Now, if you want to make this dish lighter and less calorie packed you can do this - instead of using double cream you can use stock - chicken or veg. I just use the knorr stock pots and I would use two. I then mix the stock with about 100ml of milk which makes its a but creamy. Dauphinoise potatoes are cooked in cream and you don't add cheese. Boulanger potatoes use all stock. I find dauphinoise delicious and rich but just too calorific to eat regularly so I use the stock with a bit of milk much more regularly.( Goes deliciously with lamb!). Now, make sure that your cream/ stock mixture comes up to nearly the top of the potatoes. Cover with foil, put in oven ( 160c) for about 60- 90 mins ( depends on size of dish, how many servings ). take out of oven, poke a knif in the middle and it should slide in like butter. If it doesn't then pop them back in. When they are cooked, take the foil off, turn oven To 180 and put back in to give the top some colour. You could cook the chicken at the same time. Take the potatoes out when the top is golden and - this is important - leave them to sit For ten mins with the foil/ clean tea towel over the top. You can cook them in advance- even the day before- and just cover and reheat. It doesn't really affect them. I would serve the potatoes with the stuffed chicken wrapped in pancetta with a green veg/ salad and I really like pomegranates idea of the cherry toms on the vine. You can finish the pots/ reheat at the same time as cooking the chicken and the just spray the tomatoes with olive oil and pop them in the oven for the last ten mins. My mouth is watering!!! Seriously , this is a great dish to serve and it would work very well together at this time of year. Don't forget to season your chicken under the skin of you leave it on or inside where your stuffing is going, trust me, seasoning makes or breaks a meal. You will be fine. You can cook the pots during the day at your lesisure, stuff the chicken and wrap it in the morning ( take it out of the fridge 40 mins before cooking, this ensures that it's at room temp when you put it in the oven. If you put meat at fridge temp in the oven it's easy to have the outside dry before the inside is up to temp). Prep the veg/ salad and out in plastic bags in the fridge until you are ready to cook/ serve it. Stay calm and if it helps, write down a time plan or list of steps to getting everything on the table and tick off. Then you won't worry you have forgotten anything. Good luck, let us know how it goes!!