Plants are very hit and miss with African Rift Lake Cichlids, hardy ones such as Anubias
and Java Fern
usually work, but bare in mind the fish will likely sample any plant. Africans being diggers as well, they can easily uproot plants and cause annoyance to you, having to re-root them all the time.
In terms was what you can stock, aim for 12-15 fish Maximum, something to consider along with the yellow labs would be..
Psedutropheus sp Acei, Iodotropheus sprengerae
(Rusty), Red Zebra
(Metriclima Estherae) - although note these will cross-breed with the yellow labs, Cynotilapia afra
You also need sand and rocks in the aquarium as this mimics the natural habitat of Lake Malawi, the lake has very few plants in it, mainly rocks and boulders.
You could also consider adding some bottom dwellers such as BN pleco, Synodontis Multipunctus, these would require driftwood which would also be beneficial to the fish also.
Make sure that you have adequate filtration, at least 10-15 times the tank volume per hour, these are messy fish ad will deteriorate water parameters quick without adequate filtration.