Planning to get a silver arowana.

I'm planning to buy a 250 gallon used and put a baby silver arowana in it I'm planning to probably change tanks after 3-4 years, and also does a arowana need 2 canister filters or one oversized can do?

Do these things grow massive really fast?

FYI:I'm a beginner but have owned fish

The 250 gal is going to have a strong lid