Yes, that is right. Buffs are homozygous for several recessive colour genes that we know about (dusky, chocolate and buff). You can tell that by looking. No testing required for those genes. Are you sure they only have one Blue dilution gene though? That'd be something to test for.
You already...
Yes
Personally I think that if you are going to go down the road of having these birds established and recognised as a breed then calling them Bessemers is preferable to calling them Jumbo Orpingtons. There are plenty of breeds that share exactly the same colour and pattern as other breeds...
A breed breeds true. Whether it not it's in any kind of Standard it has to breed true over multiple generations to be considered a breed. You won't know what these birds are hiding genetically till you breed a few generations.
I sympathize, but I'm afraid that you can't put up photos of a few...