Hello and welcome!
I started my hens out on Dumor chick starter/grower, and then once they reached around 20 weeks, I switched to the Dumor layer feed pellets. I do think, from watching my hens, that maybe the chick food tastes better to them, but I can't say that's a fact. I noticed that it does take them much longer to eat a feeder full of pellets than it does for them to eat a feeder full of the crumbles. I like using the pellets because there is much less waste.
My chickens are locked up in their little barn (it's 8x12) until 5pm, then they get to free range until it gets dark, when they just go back in on their own. Then I lock them up.
Regarding the treats, just use your own judgement. If the treats are nutritious, then it's OK in moderation. Small amounts that they can eat pretty quickly are OK. Now, scratch and corn really don't have much nutritional value. In fact, they're more like candy to a chicken, so I only offer corn and scratch as an evening (before bed) treat in the winter time, because digesting it causes their body temps to warm up, and they need that in the winter.
Summer's always nice because my chickens get tomatoes from the garden, and watermelon, cantalope, cucumbers...healthy fruits and veggies are great for them, and if you refridgerate them before offering them, they're a cooling treat as well.
The treats you listed all seem pretty healthy, so I think they're fine, just be sure to give them small amounts. Also, I never give my chickens table scraps because it's just not good for them....they can get fatty liver disease, and then die younger than they're meant to.
Hope this helps a little bit! Sounds like you guys are doing a great job!