This is usually caused by the cruise control brake switch. Where safe but with car on the road with cruise dropping out, can you set cruise and keep it running by lifting the brake pedal up towards you? If so, then look at the brake pedal switch and locate and adjust the position of the switch slightly so that it does not disengage prematurely.
No need to do that unless you bought some type of extra insurance for spilling water on the phone. I don’t think it would be worth the cost. Depending on how much water you spilled, there will be some level of corrosion which could eventually decrease the life of the affected components. There is a recent article on ifixit about dealing with water in phones so check it out. Good luck.
SSD is super light and doesn’t need a caddy. You can find a place to strap it out of the way with a couple wire ties. I have an old optiplex and that is what I did. As far as the 2.5 TB use the caddy for that one.
Are you referring to what is commonly called the speaker “surround” which mounts the cone to the frame?. If so, yes you can definitely replace those especially if the speaker is a common size. There is a guide on ifixit for repairing this speaker unit including replacing the whole speaker itself as well.
If you checkout the ifixit tear down of the C202 in step 8 they remove the display from the rest of the case and it looks like that plastic cover is still attached. I have seen these often as just ‘wrap-around’ pieces that can be carefully popped off of short partial shafts on either side. You should be able to flip that piece back and forth with the display detached if need be.
Please ensure that all of the display ribbon cables are properly seated. When I replaced the screen and force touch sensor gasket on the series three I had the same issue. I had to reopen the case and I carefully re-seated all three ribbon cables and then the force touch worked properly.