Go right ahead and plan for an expansion tank. A pressure tank and a pressure switch creates an on-demand pumping system. If this will feed drip irrigation, you will require filtration to prevent the emitters from clogging. A shallow-well jet pump is ideal for this sort of thing, because it will generate enough pressure to operate sprinkler heads, but not enough pressure to burst pipes if something goes wrong. You also want a pressure relief valve at the pump, for backup protection.