Re-stocking 60 gallon

[Questions?]

Hi everyone, I currently have a 60 gallon freshwater African cichlid tank featuring 8 Yellow labs, 2 bristlenose plecos, and 1 clown pleco. I'm currently in college and I would love to do something for my parents (they love the tank and look after it) and they have always wanted me to add more fish of a different variety. I did some research and really love the Yellow Tailed Acei cichlid and Rusty Cichlid. I was wondering how many fish I can hold without overstocking. I am going to give my LFS 4 of the labs so that I have a 1m:3f ratio and I was wondering if there would be room for 4 yellow tailed acei and 4 rusty cichlids (however they would be unsexed so I'm hoping it would be a favorable ratio.) There is a good amount of rocks in the tank and once I am home I will add even more to help break up the line of sight and add more spaces for the fish. Thank you in advance for the tips and once I'm home I'll see about sending pics of the current tank

 

[Questions?]

Oh forget the filtration, currently running a Marineland Penguin 350B Biowheel HOB filter but if needed I have another of the same filter sitting in storage or my dad has always wanted to get a canister filter so I can get that too if you don't think my current filter will be able to handle the additional bioload. Oh and the current inhabitants are doing not extremely well, the tank has been running for about 5 years and there have been successful fry raised without any interference on my or my parents part.