You will have less than a year before the silver arowana outgrows the tank, silvers can get to 4 feet full grown and will easily reach 2 feet in a year or less, as with many of the large predatory fish they have a amazing growth rate. If you can find one a black arowana would be a better choice as these tend not to get so big in captivity and often max out at 2 feet though they can reach 4 feet in the wild.
The time for Bichirs is now, currently it is the season for West African imports so there should be a few of the harder to find species like
P.palmas and
P.endlicheri about if you look in the right places.
The clown knife fish is again a fish that really isnt aquarium suitable with a maximum adult size of around 4 feet, you do like your tank busters dont you
While 224 gallons sounds huge within a few weeks you will soon realise its not, i would stick to fish that are not quite so huge with max sizes of 18 to 20 inches.
Also be aware that many large oddball/predators are aggressive and territorial so choose your tanks inhabitants carefull and try to stick to fairly non aggressive fish, also most will grow very fast so try to buy fish that are already of a size that cannot be eaten by other fish, once a predator community is established it can be very difficult to find new suitable tankmates. The bichirs are a good choice (provided there are no smaller fish about) and oscars are usually ok in large fish communities with the rare exception for overly aggressive individuals. Other good choices are
Sorubim lima shovelnoses which are quite common and easy to obtain, some pike Cichlids and if you are up to the challenge FW stingrays can be kept provided the water is kept good and there are no aggressive fish in the tank. there are also many other species of medium/large catfish that can be added as and when you find them.