I'm working this out as I type this, so this may be a lot of info you already know...
Amber Champagnes are E? A? CC Chch
Cremellos are ee ?? CcrCcr
Just for fun, let's assume the mare carries 1 copy of Agouti & the stallion carries 1 copy of both Extension & Agouti, the foal could be:
Ee Aa CcrC Chch - Amber Cream Champagne
Ee Aa CcrC chch - Buckskin
Ee aa CcrC Chch - Classic Cream Champagne
Ee aa CcrC chch - Smokey Black
Ee AA CcrC Chch - Amber Cream Champagne
Ee AA CcrC chch - Buckskin
Ee Aa CcrC Chch - Gold Cream Champagne
Ee Aa CcrC chch - Palomino
Ee aa CcrC Chch - Gold Cream Champagne
Ee aa CcrC chch - Palomino
Ee AA CcrC Chch - Gold Cream Champagne
Ee AA CcrC chch - Palomino
If I've done this correctly, it would make the chances of each colour 25% Palomino, 25% Gold Cream Champagne, 16.67% Buckskin, 16.67% Amber Cream Champagne, 8.33% Smokey Black, & 8.33% Classic Cream Champagne
So it looks like you're spot on.
Obviously it would narrow down the possibilities if the stallion carried one or two copies of extension & agouti & if the mare carried agouti at all.
No, the foal cannot inherit 2 copies of a gene from one parent, so it will only get one copy of the cream gene from this crossing. You'd have to cross the mare to a stallion who also carried the cream gene in order to get a double dilute.