As has already been said here, if you can't create a template for this, then it won't really be helpful for improving internal processes. I'm a coach and currently use Dubsado. I was hoping to replace it with Squarespace proposals, but if I can't do templates, then it's pretty useless because it means I have to recreate the proposal from scratch for every single client. And contracts. And they are not short.
I thought a workaround may have been to create a template client and then copy them, but even if that's possible, if you then want to pull client information in from a form, then this doesn't work either.
Another thing that isn't really functional, is you can't get the person to 'select' an option in the proposal for acceptance. So if I were to display three possible packages with different pricing, the client needs to be able to say I'm accepting for package 1 for example. Even your example text in the proposal says 'next steps, select a package', but there's no actual way to do that.