First Malawi Mbuna Tank

This is my first post, sorry if anything is out of place etc

I've never kept African cichlids before, but here goes!

I had a 4 foot oscar tank, that, after the oscar's eventual death, was just taking up space. I was recently offered a pair of Mainganos, which seemed like a great opportunity to create a mbuna tank! The mainganos aren't fully grown), are are being housed together, and are both apparently males - which from what I've read, is far from ideal, so once I get them I guess I'll be adding probably half a dozen females to even things out a little. I stripped out the tank, fully rinsed all the gravel, cleaned or replaced everything n the filter, and set it up again to cycle. A problem with the filter meant that it was turned off soon after setup, however, and yesterday I temporarily replaced it with a slightly smaller canister, which is rated to over that sized tank, but won't be sufficient with a large bioload of african cichlids. The substrate of the tank would be cycled with a good population of nitrifying bacteria by now I assume, so I added a small bristlenose from one of my other tanks today.

SO, the first of my questions would be around the set up or rocks in the tank. African holey rock, among other, was recommended to me, but from my research it is just a variety of sandstone, which I have in abundance in my area. So I went scavenging around my house and picked up a whole lot of it, which I washed and stacked up in the tank, as well as the rock I already had. Is this sandstone in fact suitable for Mbuna cichlids?
My other question is around the rock formation. I'm not sure if this picture clearly shows, but I have created a number of caves (that will remain stable as the fish extend them by digging and hollowing them out). Is this enough rock formation for a Mbuna tank? (yes, the light is a little wonky... I managed to snap off one of the brackets haha)


I also have lying around a tub full of crushed coral and shells, which was last used in a marine tank. I rinsed this out well, and am thinking of adding it all the this tank, to help with pH. Is this a good idea?

So basically, how is my Mbuna endeavor looking so far?

Thank you

The caves should be big enough, seeing as the fish will be able to dig a lot of them down the the bottom of the tank where the rocks rest. Do mbuna's dig comparably sized caves to breeding convicts?

I didn't think I had any eggcrate when I assembled this, but have since found some in the garage. Facepalm. So I guess when I'm rearranging the setup between additions to help with territoriality I'll pop that in underneath, and add the crushed coral as well

I'm definitely more pleased with the new rockscape.

I added a 3-spot gourami as a temporary inhabitant a few days before I scheduled to get the mainganos. One of the mainganos died with its previous owner, but the remaining fish is obviously a male, and has been settling in for about a week. Despite being much larger than I had anticipated (at least 10 cm (4 inches), he appears to be a massive wuss, constantly hiding in cave in the far left corner than he has staked out and done a lot of digging in - he rarely comes out, and only then for food within a couple of inches of the entrances.

Yesterday I added 2 more small mainganos, and 3 electric yellows. So far they have been a lot more active and sociable than the much larger male, and there has been minimal aggression/territoriality between the cichlids, If anything the gourami is keeping the smaller fish in line.

Current stocking is as follows:
1x mature maingano (male)
2x small minganos (potentially females)
3x yellow labs (unknown)
1x 3-spot gourami
1x small bristlenose

Thoughts on tank arrangement and rockscape, stocking, and any other suggestions for the future would be wonderful, thank you