2n7000 are logic level and can sink up to 100mA.
As for limiting resistors, for this discussion let's assume you're multiplexing the rows (displaying 1 row of 8 columns of LEDs at a time). You'd put 1 resistor on each column, so any LED that is lit on the same row will receive its own current from its own resistor independent of the other columns. The rows share the resistors, but this doesn't matter since only one row will be active at a time.
Since each column would only be driving 1 LED at a time, if the current drawn by one LED is within the current limits of 1 PIC I/O pin, you won't need transistors on the columns. The rows, however, could be driving up to 8 LEDs at a time, so the row pins would need to supply or sink 8 times the current. This is why the rows often have transistors but the columns don't (or vice versa). See the . His don't have any transistors at all, since he's driving the LEDs with low enough current to stay within a PIC's current limits. But if you want brighter LEDs, you'll want transistors driving the 8 rows. Either NPN or N-channel logic MOSFETs will do the job. NPNs are cheaper but you'll need base resistors which you won't need with the MOSFETs.