For your purposes that power supply will be fine, for a four lane club track I would recommend a minimum of 10 amps however.
I have never seen a Ninco powerbase, but I do have a skidpad made up of Ninco track. I made up some clips like this out of phosphor bronze from the K&S display at my local hardware store, they fit into the underside of the track rails.

Track polarity is a confusing subject, it refers to the direction that electricity will go through the controllers. Set type tracks are wired for what we call negative polarity and most club type tracks are wired for positive polarity.


You can switch from one scheme to the other by switching the wires to the power supply and also the ones that go to the track rails, the cars will still run in the same direction.
If you only use resistor controllers it does not matter which scheme you use. If you wanted to use an electronic controller, electricity can only go one way through those, so you would need a controller that matches your track. For aftermarket controllers the positive polarity type is the most common, there are also a few dual polarity controllers available.