Tigers are known to focus nipping between themselves when they are in a decent school. But still I think its a bit risky with the guppies. Also with the stocking, the silver sharks they get to a foot long each are very active and need to be in a group of at least 5 as they are a schooling fish. Other thank that your tank looks okay
As for adding more cichlids, you could look at keyhole cichlids? Or Cupid cichlids maybe if you want something a bit different - though you need a sand substrate for them. A Firemouth or Ellioti could work in there as well, though the guppies could become food.