Why don't you look into fishless cycling with ammonia instead of adding fish? Potential spikes will be a problem as you would need to do large water changes to save the health and long term well being of the fish, and in a size that large, it will be a chore. Ammonia and nitrite are not much likely to kill a big fish but they're very likely to trigger disease outbreaks 4-6 months down the line....
If you fishless cycle, you could nearly add what you want at once without worrying for spikes, once the tank completely cycles. This can take 7-8 weeks. I think its a bit too soon adding fish....
While waiting to add fish, think about some decor....emersed plants for example, aquaponics set up, etc...The suggestion of bog filter is good but you could just have some plants sitting their roots in water. The plants will look pleasing and help water quality too tremendously. Have a look at my mini pond below, not difficult to do...These are planted in hanging baskets filled with clay pebbles(you need to soak the pebbles first or they'll float). I've had plants like that in my tanks for years and it does play a big role in water quality, though I don't keep monster fish. No maintenance required for the plants, and fish can't get to them....
Also, you do need a 2nd filter for redundancy. I would never rely on just one filter.....