Psst. If you decide to go with Sisters eventually, you might consider supplementing them with a few figures from Wargame Exclusive. They've got some cheeky "alternative" models to...uh...'spice' up your army. 
https://wargameexclusive.com/
For reals though, vendors like that actually have some pretty neat extra bits and bobs to customize weapons, vehicles, armor, etc. But man....the minitures hobby sure can develop into one heck of a money pit though.