Have you submitted to professional publishers to see if they will take it on? (And so make this someone else's problem.)
Selling off your website presents all sorts of problems - it's technically easy but practically problem ridden. Or, at least, that is the wisdom that others have submitted here previously, very convincingly - to the extent that I have never been tempted to try it. (
But I publish standard narrative fiction, so I fit into the more attractive offerings from Amazon.)
Have you considered serialising the work? Breaking it up might offer several benefits and might perhaps let you in for better options at Amazon?
Have you taken a look at
Smashwords? I have no idea how they would handle a work like this (quite likely their "meatgrinder" process would make a mess of it), but it could be worth a look at their non-fiction section to see what others have done. But, the main reason for mentioning them is that you might get some inspiration for wording from their style guide (see their How to Publish page).
Given the material I can understand you using PDF, but this will probably constrain your audience to desktop and tablet (rather than e-reader). That's probably a realistic expectation anyway by the sound of it.
In terms of book size (the 450MB). Do make certain that you experiment with your options here. Make sure you are using the correct image format for each image type, and for JPEGs experiment with lower quality settings - it is often possible to halve, or better, the file size with little to no human visible defects.