It all depends on the cichlids. There are several types of cichlids that can live with corydoras, danios, and harelequins, and some that can even be kept with neons and cardinals. If you can do it right and start keeping your schooling fish in schools, as well as decorate the tank properly, and choose the right cichlid species, you might be surprised what many cichlids can be kept with, as would a lot of people who just assume cichlids can't be kept with anything at all.
I have nicaraguensis cichlids in a 75 gallon. The male is 8" long, the female 5" long. The pair are kept with a school of 10 serpae tetras, a school of 12 redtail rasboras, and several cuckoo catfish. It's a stunning tank and it's so cool to see that big fish swimming amongst all those little tetras. I chose this species for the point of making a community around them and it worked better than I imagined, but everything was done with forthought - one species for the middle, one species for the top, one species for the bottom that would eat the cichlid eggs and prevent spawning, one pair of cichlids that keep their aggression among themselves and are not built for eating fish.
Fish take research and knowledge, but cichlids take even more so because there are more types that won't work with community fish than will, and also because there are professional and amateur ways to keep them and set things up and establish proper pairs and groups.
I hope you understand that every fish you have except the shark is a schooler and will only thrive and show their best and most natural behaviour in numbers. When you start adding fish like cichlids to the mix, keeping the fish in bigger groups goes from being important to being absolutely vital.
The shark is going to present the biggest problem with the cichlids because most cichlids are territorial and so is the shark - they could end up fighting over space. Still, it's possible to do if you set up everything well. Coolie loaches are shy and not strong at all and I would not keep them with any cichlids, except maybe rams. Cory catfish can work surprising well with calmer types of cichlid, even big ones like Severums.
Check out www.cichlid-forum.com to learn more about them. There are articles, a great forum, and some recommended setups for various sized tanks.
Although there are some African river cichlids that can work, do not even think about going with African Rift Lake cichlids - they have very unique needs and behaviours and have nothing at all to do with new world cichlids except the general class of fish they are.
Anyway - look into Severums - they get big, but are not overly aggressive and can be kept with most of your fish once you get them into proper groups. Neons and cardinals might be a little small, that's ok - just get an even bigger group of harlequins instead so they can thrive. Even the coolies might do ok with them - it's a risk you can chose to take.
