Having multiple heaters instead of one giant one is pretty normal for a larger tank. Get whatever is your fancy, they're all bound to fail at some point, so it's in your best interest to replace once a year or so.
Multiple titanium heaters. It’s mostly dependent on room temp. If room is very cold, you’ll need more. I imagine 500-1000 watts (Total) will work. You want to have enough power to not have to keep the heater running 24/7.