Depends what type of 75 your doing. A FOWLR tank, IMHO, maybe 1 or 2 more. Reef tank, your about maxed. I forgot to throw in, are those percs or something else? 2 percs is approx. the same bioload as 1 full grown flame angel. 2 full grown tomato's or 2 full grown maroons would be equal to 2 full grown flame angels as far as bioload.
Totally your choice, adding a skimmer doesn't automatically mean you can increase your bioload. For one thing, if the skimmer fails, now what? You'll have a overloaded tank while waiting for a replacement. If it's just wnating to get more fish, time for a bigger tank or start up another one (nano maybe) .