Well what do you really plan on doing?
If you are making large displays 5x7 clusters can help reduce
wiring. The idea is is to create matrix (rows and columns) and
refresh frequently (faster than eye can react).
Since the most clusters are only 5x7 LED high, think about arrangement
and scanning to get higher duty cycle for all LEDs. It means that
if you go with say ten 5x7 clusters you would get display 7x50 (HxW).
Although it is simpler to scan columns (each column as one byte),
it would be better to do it in rows so the duty cycle of LED which is on
would be some 14% instead of max 2%.
The lower duty, less brightness from the LEDs. Sure you can use
higher drive current (well you would probably do it either way),
but it is safer to keep it down - LEDs are moe likely to live longer
and if your PIC gets stuck (program error or whatever).
If you are not interested in that big displays, consider using
character or graphic displays. With background lighting and
good selection of colors they can be very atractive.
This would also mean much simpler interface (fewer I/O pins)
and lot's of code samples to choose from (you don't want to
reinvent the wheel, do you?).