1)
Susannah has always been one of my favorite names, it's feminine without being frilly and classic but still unusual. It has a variety of nickname options too, never a fan of
Susie or
Susan, I've always liked
Annie or
Anna.
2)
My favorite combinations are:
Susannah BeatriceSusannah RuthSusannah BelleSusannah PearlSusannah CatherineSusannah Lily ( I saw you all ready mentioned this...)
Susannah Poppy ( in keeping with the flower theme)
Susannah Fleur ( also flower related)
3) Most classic names go well with
Susannah. I've always liked the combination of
Susannah and
Adeline. Other suggestions:
For girls:
TheaClaraMadelineAudreyPhoebeCarolineEleanor
Boys:
HenryThomasIsaacMorganGeorgeJudeLeo
There aren't many names that would clash with
Susannah. Two very feminine, longer names ending in "a" might be a bit much, or a very modern, trendy, or masculine ( for a girl) name wouldn't go as well with
Susannah but most names as long as they were somewhat classic would sound fine.
Hope that was helpful!