Hi,
The Starter board, though small, does allow a little room for you to add on a few extra bits of your own hardware, but the chip fitted does not allow you to use the Debug function of Mplab, though it is not necessarily a feature a beginner would want to use.
The Debug Express is really small, about 3cm square, and has all smd parts.
It is not an easy board to expand.
Both are good boards to 'get you going' but you will soon find your will be building you own larger boards.