i would stick with the 4 syns. they may pair off leaving you with a breeding pair (or) two in there already. If you must i would add a single male of the types you mentioned.
a flower horn would be fine, by itself yes, in a pair no (unless divided)... may not peacefully coexist with the syns tho. but it not unheard of it being done before
a flower horn would be fine, by itself yes, in a pair no (unless divided)... may not peacefully coexist with the syns tho. but it not unheard of it being done before