From the Kickstarter Page: "...We will collect this via our pledge manager after the campaign ends..."
Certainly yes to questions 1 and 4 (all KS pledge managers where I participated in had those options).
Late plegde and upgrade: Late pledge is "usually" possible, but it depends solely on the publisher - the uprade usually not (since KS automatically adds your chosen reward fixed to your invoice), but you will surely be able to add an additional champion pledge.
Thank you for the response. I wasn't able to back this game this time around, but I may be able to later if they allow late backers.