You'll get both source and image files for all doodles.
Yes, if you are ordering Basic or Standard package then you can pick any two or three from given four options, i.e. New Year, Halloween, Thanksgiving & Christmas. Pro package includes all four options by default.
Doodles are created using a standard manual process which makes it very difficult to accommodate custom feedback. At the maximum, we can accommodate one revision assuming it doesn't result in change in original logo design in any way.