Regarding items
Items 1, 3 - Model S of this vintage has both front and rear induction motors versus Model 3 with a permanent magnet motor. One of the key differences is the PM motor being able to provide a braking torque at zero rotational speed which isn't really possible with an induction motor without a excessive heat build-up that's not good for durability. This is where this vintage Model S doesn't really allow what some call true single pedal driving. You ultimately need to press the brake pedal to bring to a complete stop.
This may be a part of what you call "loose" feel, but also need to recognize the S is a heavier car, so even with the exact amount of braking force, it will not decelerate as fast. That's simple physics of higher mass/heavier car.
Regarding what you term "handbrake", I'm guessing you may be referring to the brake hold feature? On the Model S, since it cannot do true single pedal driving/breaking, there is brake hold feature. WIth this after you come to a stop you firmly press the brake for a second, will see an "H" type of icon come on the dash, at which point the service brakes are engaged to hold the car even if you take your foot off the brake pedal. Soon as you step on the accelerator the brakes will disengage.
Coming from a Model 3, and likely not being accustomed to having to touch the brakes to stop, you may view having to set Hold mode as taking an extra delay, but as someone that has driven an S like this for almost 7 years, it becomes automatically really quickly and totally an unconscious action.
Item 2 - light steering.. There is a different driving dynamic between the S and the 3. If you read many early comparison reports from when Model 3 first introduced you'll find a couple comments where people describe the Model 3 as more "nimble", faster/crisper steering feel but at also harsher ride/stiffer suspension. Ultimately that's a combination of Model S larger, heavier, tuned more as a touring car versus Model 3 small, lighter, tuned with a "sportier" handling feel. Continues to be one of the reasons some prefer one over the other.
Item 4, 6, and 7 - I'd make sure to confirm if this car has MCU1 or MCU2. All of these can be symptoms of car with MCU1, especially if the eMMC chip has not been replaced and starting to have more and more "dead" memory addresses. If you don't already know how to confirm this, pull up the "more info" link on the main screen. If the infotainment processor lists NVidia Tegra it's MCU1, MCU2 will show Intel Atom. Issue with navigation map responsiveness ultimately become one of if not the key reason I decided to invest in paying for the MCU2 upgrade on my 2016 Model S. That's especially true if you have display set to satellite view.
Item 5 - defective volume control wheel is obvious just something broken on this car and needs to be repaired/fixed. Either ask that be fixed as condition of sale or negotiate appropriate price reduction.
Just my two cents worth.