Hiya
Yeah you will have to make some changes, I had to as i was supposed to have another tank but it fell through, so i changed to malawis anyway.
The Ph may be lower depending on what you have in the tank, generally it is. ie I had bogwood in my tank so out this came.
Temperature wise, it should be around the same but check out the species and again it depends on what species of African cichlids you are getting.
You will still be able to keep the likes of your plec, and this will help you out with the algae.
As for plants then you may aswell kiss goodbye as theyll get ripped up straight away, although some keepers do have plants in theres this I have heard is the minority. Rocks need to be arranged so plenty of hides and caves are made, You can stack them and leave them loose, or like i did and bond some small structures together using milliput.
You may have to change the substrate although i didnt bother and kept the pea style gravel, this hasnt been a problem and has worked successfully
The diet will change slightly so you will need to learn what their main area of food is and i have learned the key to feeding is variety AND dont overfeed them even if they do appear at the glass looking hungry.
Check out the pinned article on keeping Mbuna Malawis if these are the fish that you have decided to go with.
If you need any more help there are other more experienced people on here than me but if its an emergency and you cant wait and im the only one online drop me a PM.
Good Luck with the project