I'm planning on building a pond next spring about 4ft * 4ft and 2-3ft
deep. I wont be having any fish just a fountain in the middle. I'll
have 2 rows of paving slaps round the pond as it will be part of a
patio/terrace.

My questions are

1) will I need a filter if I dont have fish

2) How do I get the pump\lights cable into the pond. Is it usual to
run it under the paving in which case what about maintence. I plan on
having a junction box at the edge of the paving 'hidden' by plants.