Well, I think the reviews were probably bought, but that's not uncommon when a seller first starts out on Amazon. You haven't overpaid in my opinion and I'm sure most of it will sprout and grow. That's a nice mix of seeds!
Have you designed your layout already? Keep your chicories separate if you're planning to save the seeds. They will cross-pollinate otherwise. Endive and escarole aren't the easiest to grow. They need blanched and have fussy watering needs, but they fetch a good price, so it might be worth the hassle to you if it pans out. Your kale will likely collapse dramatically at least once when it's been particularly hot outside, but it should recover once the sun goes down. Just give it a little water.
I can tell you've done your research, but don't spend a lot this first time! Don't build anything permanent if you don't have to. Who knows, after this first experience you might decide to move your plot to another section of the yard, or you might decide to take it inside, or switch to hydroponics, or something else. Heck, you might hate the whole thing and decide that gardening for profit isn't for you. So many people go all in and regret it afterward. If your soil is good, you probably won't need whatever a "feed insert" is. You haven't depleted the soil or anything yet. You can also overfeed plants.