The biggest issue I would have is the costs for the upgrades would be a prohibiting factor. Lots of "wasted" money on the smaller tanks when I would try to go straight to the largest possible.
The equipment used to setup the 20 would work OK for a time on the 40, but when going up to the 125 and then the 280 is going to be a lot of new equipment both times.
If your end goal is to end up with both a 125 and a 280 then this might not be such a bad option, but if the end goal is to have one 280 gallon tank, you are "wasting" a lot of cash to get there.
Selling off used equipment as you "outgrow" it can also work, but there are a lot of variables with that too.