Need help with new interstate and intrastate trucking

Yes, for the truck traveling out of state. Local truck wont need an ELD if you're within 150 mile radius

No, both trucks will run under the same DOT numbers. They both belong to the same company that the DOT number is registered to.
You will need to add all the states that you will be running that truck in, to your current authority/DOT registration. Both trucks will be allowed to run those states, but dont have to. So, the local truck will be apportioned for those states but will only run in state.
Most people just add all lower 48 states... just in case but you dont have to. If you know you will only be going to 3 or 4, or even 10 states, you can just add those states if you'd prefer. Again, most people just add all 48, just in case.

Incorrect. The home base is where the office & records are kept. No matter where the truck goes, its home office is where the records are kept.

I'm not the expert, so I welcome any corrections to any incorrect info, from the pros.

 

Thank you for bringing that up. I actually wondered about that. I've never registered a commercial vehicle for local use only. I wondered about that.
I just wasn't sure if he was running just USDOT numbers or if he already had his MC numbers... or, like you brought up, anything at all. I was just assuming he already had his USDOT numbers for local stuff.