should only need a dot number if it is used for a commercial purpose
You need to be more specific. If it's for private use, is it a registered farm vehicle, recreational vehicle, or other vehicle exempt from classification as a commercial vehicle under FMCSR? In those cases, no, you don't. You might, however, be required to display "Not For Hire" on the sides of that vehicle.
There's no logo requirement on a commercial vehicle. On a Class 8 tractor--a semi--you need the license plate (base plate) and either a DOT number or "not for hire." You can put "not for hire" on a truck that is not used in commerce, like the tractor that pulls a race team's trailer. Everyone else must have a DOT number. But as far as logos go, you don't need to have a logo on your truck.
ask a gas station they should be able to help
Commercial trucks with a Gross Vehicle Weight Rating of 10,001 lbs. or more. So, basically, a one ton pickup and larger, when used for commercial purposes.
Yes. However, whether or not you're able to pass a DOT physical and obtain a DOT medical card (which you'll need in order to operate a commercial vehicle) will depend on how severe your condition is.
You need to have the number displayed, and documentation of the validity of the DOT number.
A DOT Reportable Accident is an accident where any injuries occured or any vehicle involved was towed from the scene. Additionally if there was $10,000 or more in property damage.
If your vehicle is engaged in interstate commerce.
What's to know? You're out of service, so it's clear you were in violation. Either it'll need to be repaired on-site, or towed to be repaired.
No. A vehicle is commercial in nature based on its usage. More the same with classifying it as a Commercial Motor Vehicle (CMV), which requires an FHWA annual inspection sticker, registration as such, and DOT medical cards if used in interstate operations. Stack size does nothing to change the manner of use or Gross Vehicle Weight Rating of the vehicle.
Typically it is the DOT and PSC (Public Service Commission)