Africans are 100% not brackish fish at all..
For keeping Africans your water is fine, no problems with that, pH is nearly perfect for them.
You can use crushed coral to buffer but if you are considering keeping Africans, then sand is a better substrate as that is what Lake Malawi is naturally.
Research what fish are available local and if you are prepared to order online as well.
To give you a nice color tank, you would be looking at 4 species with 5 fish from each species in a 1 male to 4 female ratio as maximum for a 75g tank...if the fish are juvenile then 6-8 fish if they are small until they are old enough to sex (which is quite difficult to do).
Look at Pseudotropheus sp "Acei" and Labidochromis Careleus (Yellow labs), Red Zebra, Cynotilapia Afra and Rusty (Iodeotropheus Sprengerae).
Also Synodontis Multipunctus / BN Plecos as bottom dwellers and in tank vacuum cleaners
(about 5-6 of either one)
Check out other fish as well but check on here as some fish are extremely aggressive and not suitable for beginners into mbuna.