To determine these factors first of all take "single" photos and not in groups.
Secondly, this is not a huge collection and no it's not worth millions of usd.
a bit like what happens to me when they ask me for my opinion on a collection it is good to be very clear
right awayI don't know which ones you have seen that have these ratings (400K USD :O ) but unless they are "misprints" or particular runs, the ones you have shown are very common.
For example, I see many examples of 1c Benjamin Franklin, Scott n. 300 issued in 1902 (photo 1-2-3-7-8-9-14-15) from the catalog is 0.50 usd (perhaps on postcard or envelope support it can reach 2 USD).
it's enough harder finding a buyer some times because these are really commons (and not in "perfect conditions" like photo 9)
Maybe you can have some rare use for cancellation/destination but its.... rare.
Use this site for an idea https://www.kenmorestamp.com/us-stamp-identifier
