Continuing the discussion from Banner images cut off :/:
Oh boy. This is not good. I'm afraid it'd be more expensive than (I guess) anyone would be willing to pay.
All that sounds to me way more complicated than they should. I mean, I I were a squarespace customer who knows nothing about programming or how websites are built, I can easily see how frustrating this can look. "How come we can do all that on the page, but not on the title?" I would ask myself. It's quite an unfortunate limitation indeed! Except maybe for the popup, that is not really provided.
In any case...
Adding a popup message is simple enough, I've done it before. "Building" a form inside it to leave an email addres is much more complex and not so trivial, although it's also not too hard to do. The tricky part is how to add content, like with the video banner. The same for making the 4 buttons across the header.
The total cost would be U$444.