I have a 46 gallon Bowfront.
A nice tank and great beginner tank.
The size will be easier for the beginner to care for, Not too small so harmfull water conditions build up too fast yet not too large that it becomes more of a chore to keep clean.
That is a pretty good sized tank to start with. It is good to see someone doing some research before hand! Just make sure it is big enough for the fish you are wanting pacu and arowana are couple that come to mind.