There will be mixed opinions about stocking, because everyone does things differently. I'm going to be different and tell you that every time (except for the case of one super-aggressive male murderer angel) I have had an angel alone, it withered away and died within a few months. Just stopped eating and was really nervous and hid all the time. I've had hundreds of angels, I used to breed them. They just really do best in pairs or groups. Maybe you've got one that's ok alone, a few are. But mostly they are very social. You will get just as much aggression from a single angel as you will from two unmated angels. The issue would be if your two paired. However, you are very stocked in there as it is, and two adult sized angels would be cramped in a tank that size with the other fish too. You probably should not keep two angels and two gold gouramis in a tank of that size, just one or the other, as the gouramis can also get very large. But I'm an overstocker myself, so I would probably be tempted to try it...but I should be responsible and advise you not to...or... if you do, check your water parameters often, do regular water changes (I do one big one weekly), plant heavily, and have a place lined up to put excess fish if it turns out to be too much.