Put stone or a couple of bricks in the bottom of the pit to support the pump.
Skip the premade container. If you need lining, lay some concrete bricks around the inside without mortar. Try to key them so they don't collapse inward. You might want to dig out that dirt a bit but I would leave it alone unless it collapses inward.
If you don't have water coming into the floor anywhere, then you are ok. If you have wet floors, then maybe you have a problem with getting enough infiltration to collect the water under the floor. That dirt looks pretty solid.