I would use a 30 long before a 29..You need footprint for sumps not depth...
What pump are you going to use ?
A ball valve is a good idea to be used but hopefully won't be needed .
I use the Jeboa DC
pumps that are digitally controlled so I can slow the flow and save electricity if I need or want to.
To start up fill the tank till it overflows into sump. Let the sump become filled to about 2 inches from the top .
Then turn sump on.After a couple minutes of running take a marker or tape and mark the level the sumps water is at[while running].This is THE MAX FILL LINE for the sump while running.This will prevent the sump from being to full and overflowing in the event of a power failure..Return pump lines should not be submerged in the water or they may syphon back more water then the sump will handle [overflow]....Make sure they can catch air and break syphon by shutting pump off a couple times..
Some drill a small[1/8"] hole on the inside of the elbow on the return pipe and that works for them..