I agree with Winegrower in concept, but you will learn an awful lot from this 400 that will serve you well if you upgrade in the future. And you can always sell it to finance a newer machine.
The lumber will have a tendency to absorb and then release minute amounts of atmospheric moisture (Oregon City near the coast?), which will move the level around some. But not the end of the world. The short Logan beds are pretty stout and you'll just have to check once in a while to keep the twist out.
If I understand the 'bounce', some woodworking machines rely on motor weight rather than a fixed tension on the motor belt, but most metalworking machines don't. I'd try it for a while, let the motor rev up and get the spindle moving before putting on a load, and see how it performs. Then decide if you need to upgrade the motor mount.