you can keep him in a 10 gallon tank (until he gets big). 10's have thin glass so as he approaches 4 inches or there abouts... you might want to start thinking bigger or aryclic tanks...
pass on the drawf lion. they are still way too large for a 10. They really need a 40 or better.
mine seems to like krill and to date has left pretty much everything alone but he is still only 2 inches long.
i wouldn't put anything else in the tank that you didn't mind loosing. go for a damsel or two. but at somepoint they may be fodder (though less likely with a smasher).
hth,
jg