Robert, what type of advice are you looking for specifically? Looking at your pictures and notes, I can tell you that the note about the HVAC duct needing to be supported with 2x4's is typically not needed. that duct should be fastened to the joists above so if you remove the 2x4 under the HVAC duct it will hang just fine since it most likely is supported by straps above to the joists

Are you planning on removing the entire wall? you should be able to. That wall is not load bearing, so can be pulled out entirely.

The 2x4 on top of the top plate that is "off center" is drywall backing, it is what they used to allow the drywallers to screw that sheet of rock to at the corner

The doubled up joists "every 6 feet" could be a couple things. There could be a cantilever upstairs and that could be the first and last joist of the overhang. It could be a headset for some havoc or plumbing. It could be that there is a load above it that needs transfers below. Could have a load bearing wall above it. Either way, it should not have any effect on what you seem to be trying to accomplish here.

You will need to either re frame around the 2 - 1/2" copper water supply lines or move them inside the wall so they don't stick out into the room

Thanks for all your advice. I am moving the copper lines as well as the pvc drain lines from the master bath upstairs.