Willyp gave good advice, as he said koura are apparently exetremely sensetive to dechlorinaters.
You can have all those together, just make sure they all have plenty of hiding places.
Make sure you keep it below 20 degrees, with a banded kokopu and inanga you'd be best off getting a 4 foot tank. If you got a 200 litre you could probably have a banded kokopu, 5 or 6 inanga, 6 or 8 bullies and a couple of koura, as long as you keep it cold and oxygenated.
Chillers are the best option, some of us use bottles of ice (can be time consuming, I currently only have to do it once a day but I suspect in the peak of summer I'll be adding ice between 3 and 4 times per day. So if you don't think you'll be able to keep it cold, you could build a summer pond for them (well shaded) and have them inside for the rsst of the year, but as long as you add enough ice you'll be fine.
You haven't asked about feeding? Have you already read about it? Or are you assuming they eat commercial food? Natives can be really fussy, heart is the easiest staple diet, I've found they like softer meat, all my fish dislike ox heart(will still eat it if hungry), they like sheep heart (will eat it til full), love poultry heart (They will keep eating til they physically can't force anything else in). The best possible diet is live bugs, garden, pond or flying they're not fussy (about bugs). But finding (or culturing) enough food is almost impossible.
Also add your area someone local might be able to help you find some fish.