I don't know how much 4 chars are, but it does get less expensive per char as you get higher in numbers. Many brides have had 4+.
The list of chars in the above post are not the only ones you can get, they are an example. You can have just about any char with a few exceptions. You cannot have any Winnie the Pooh chars, Dopey is the only Dwarf that is able to make appearances separately for the other six, Stitch is limited in the settings he can perform in, etc. Your best bet is to ask your SM/EM if there is a particular char you would like to have. Chars not on the list that have been at weddings:
Suzy and Perla (girl mice from Cinderella)
Fairy Godmother
Cindy and Prince
All of the dwarves (as a group)
Also, to answer the question about the MK photos, Disney strictly limits the photo session to you and your spouse, unless one of you is disabled and requires assistance. They are VERY strict on this. I had inquired if my sister (and MOH) could come, just to arrange my gown, fix my make-up.hair, etc, and was told no. The photographer will help arrange your gown.
If you really want to have some photos with your DD in them, then you could have the family park photo session with her on one of your days there.