Typically they are. Get one bigger than the other so they are less likely to fight over which gets to be the female. Have no more than two as the mated pair will kill the other one. The chromis are cool! I've never had one personally but I think they might be a little territorial (make sure you check) so if that's the case add him last to give your other fish time to establish themselves and get settled. Making a list is smart of you so you know who to add first and who last! Add one fish at a time. The clowns you can add together just make sure to check ammonia levels so if they start to go up you can do a small water change. You may look and see what each of them eat too.
Do you have a qt tank? You could get a little one or a Rubbermaid tub and hook up a power head or a filter etc. If there is one thing I cannot stress to you enough this is it!!! Assume all fish you get have ich because lots do! I personally pretreat them with meds as directions say to. Once that's done, if all looks good, acclimate them to your tank slowly and add them! Once your tank gets ich, in order to get rid of it, you have to remove all the fish, treat them, and house them separately until the life cycle run through.