if your tank is a full-blown reef, it depends on how it's aquascaped. even a small adult volitans is a 12" cube in size, so consider turnaround room. if you go with a
volitans, only one will fit in a 100, even if it's not a reef. if you want a very similar fish, look into
P. russelii (Russel's Lionfish, usually sold as "red volitans") as they max out at about 10" cubes (just make sure you get a properly ID'd fish).
a pair or trio of fuzzies would be SWEET, you can even look for different color morphs (red, brown, yellow). you just need to make sure you get one male to one or two females. adult male dwarf fuzzy lions have a larger head, longer pectoral fins (the fin tips reach past the caudal peduncle), and have between 6 to 10 dark bands (stripes) on their pectoral fins, while females have only 4 to 6 stripes.
D. zebra isn't sexually dimorphic, so getting a pair or harem is a crapshoot.
you could also look into some of the medium-bodied lions, such as
P. antennata,
P. radiata, or
P. mombassae.
our Mombasa lion is simply gorgeous (we found it mis-ID'd as
P. miles):
give Frank Marini's
Lionfish Care & Info Article a read if you haven't done so. Frank's new book
Lionfishes and Other Scorpionfishes JUST hit the stands, and it's a really great resource as well (BTW, that's our
P. volitans on the cover!).
you might consider multiple med/dwarf species as well, as they typically get along fine. here are our sub-adult
D. brachypterus and
D. barberi sharing their digs: