coldwater fish grow slower so i'd do a coldwater combo unless you can get the larger tank set up and properly cycled within a few months. Musky have a mountain or red tape to aquire with the possible exeption of tiger muskie. But those are rarely made by fish farms. if you're guarenteed the pike and have the proper permit to own the pike i'd get the bowfin because they have far less red tape and often no managed season, so they're easier to aquire. If you must do tropicals i'd get the armatus because they are not borderline impossible to aquire like your other options and stay smaller then the true behemoths you want, but they are pretty aggressive with one another so you might need more then 2 or preferably just 1, it will last longer in the 180. they need warm water with enough current to replicate the white water they are found in. You'll need to provide plenty of swimming room as well as cover, especially for juveniles. Many armatus and tigerfish die when they get stressed and slam full speed into the glass. for both options you will need around 800-1000 gallons bare minimum to keep the adults. but I would go larger still if you want more then 1 or 2 fish.