sump question

No such thing as too big and there are a lot of external pumps that can pump over 13 feet. I have had good luck with pan world pumps marine depot sells them

 

As long as it will fit in your basement you can go as big as you want....

 

Another limiting factor is make sure you can afford to do proper water changes on the volume of your whole setup.

 

Ill agree with all above go big that way when u upgrade to a bigger dt you set.

 

There isn't really much of a rule of thumb as to what is too big, but IMO realistically more than 2x the size of your display water volume is about the limit. More than that and the maintenance costs will start to outweigh the pros of having the added water volume. A great way to size a sump IME has been to simply makie it big enough for all of your equipment and for you to COMFORTABLY get around inside to do maintenance. There is nothing worse than a sump that is so cramped that it poses and added inconvenience to keeping up on the cleaning!

 

If downstairs means in a basement, you might want to consider how much humidity you want to add to your basement.