Welcome to Android Central! I have a Lenovo Tab 4 8" that got updated to Oreo as well, and I'm not sure why the settings are difficult for you. Is it because there are more subcategories for each settings category?
You can change the icons by long-pressing any blank part of the homescreen, then tapping Home Settings at the bottom. Then tap Change Icon Shape -- there are 4 options. If you don't like any of those, then consider installing a 3rd party launcher like Nova, which allows you to use any of the hundreds of icon packs available on the Play Store (and Nova also allows you to modify the homescreen interface in a ton of ways).
What do you mean when you say the bottom bar doesn't work right half the time? Are you talking about the Favorites Tray, or the Google search bar widget, or something else?
To answer your main question, I'm not aware of any easy way to roll back the update. You'd have to root the device and flash the previous firmware (which I wouldn't recommend if you're a novice). Also keep in mind that the system update also included security updates, so rolling it back could weaken your device's security.