The real problems with the 4 car powerbase are the lane changers and lap counter.
Both require power to operate and will reduce toy usage to maximum of 3.
Three cars is ok though but sport track appears to conduct better than the old track,
which is also shallower.
Have seldom used jumpers on even large tracks
but do use light vasoline on the rail connectors.
Always keep track flat and clean,
mine is always covered when not using.
So to sum up, 4 car base will work with couple of changers when running 3 cars,
but not more.
However if later you switch to whatever 6 car base is available,
you can use 4 car base off track to fast id chip.
Four car bases can be had cheaply on net but power supply may cost retail.
Then with current advanced 6 car base you will only need to purchase 1 more power supply.
Personally you might want to build a separate smaller digital setup to see if you like it
before switching big track to it.