Can I repaint after applying the finishing coat, since it turned yellowish?

You probably turned the blue light filter on, also called "night mode." It is a little moon symbol in the menu. Press this button again and it should go back...

I wouldn't recommend it. I'd take it to a professional who can handle that kind of thing. Refinishing a guitar is pretty tough. I tried to do it once and...

You should do both. Washing your face first gets rid of the excess dirt and oil, making the mask more effective. Washing your face afterwards gets rid of any residue...

It is best not to mix unrelated products. Mixing most lacquers with most kinds of paints doesn't usually work well, unless the product manufacturer states that it can be done....

It's best to wait a full day between coats of paint, especially if it's a heavy coat, as environmental changes can cause wood to warp.

Of course! This would require a wood primer to create a smooth finish, though. You can sand the surface smooth, apply an oil-based primer and then an oil-based paint.

If you are showing any signs of infection, such as discharging pus, you should contact your doctor immediately.