I'm about 90% I'm in the clear but I wanted to confirm with people in this community:

I'm taking my Sony FX-1 with wireless lav and a wired mic to capture the inauguration from the ground and interview passersby. DC = public property, so I shouldn't need a permit to film in this respect there right?

Cameras and camcorders of the professional variety are allowed according to inauguration security, and I've researched thoroughly the process of obtaining release consent from interviewees, thanks to this forum!

Cameras and camcorders of the professional variety are allowed according to inauguration security...

Since I do not know where you got this information I cannot comment about it. You might want to verify the veracity of the source document and read the specifics very carefully.

I'm not a lawyer nor do I have any legal training but what I'd want clarity on is whether the venue is considered public since you need tickets to get into it. This question may be moot if rules about cameras and filming are spelled out on the ticket or in a companion document.