Standard pallet rack frame depth is 42". 24" depth is about the shallowest made, 48" the deepest. Subtracting 4" gives you a rough idea of the between the beam spacing. With a typical 3000lb. per shelf capacity, it is pretty easy to set up a hoist to lift anything heavy up into the racking between the beams. Beam lengths from 8' to 12' and frame heights from 8' to 20' are commonly available. Placing racking back to back can be used to achieve even greater depths. Beams commonly have a "2" deep lip on them which allows 2 by 12 boards to be used to deck between beams if standard pallet rack wire shelving doesn't meet your needs.
This racking is set high enough , that I could drive my F250SD 4x4 crew cab under it, and even un-anchored it is still super stable.
Tough to get the strength, stability and flexibility building shelving out of 2x4s and unlikely you'd be able to knock it down and move it when you stop renting and move your operations.