After reading the posts here, I gather that I have to lay the network cables in a separate PVC pipe to my electrical wiring.

However can I lay several network cables in the same PVC pipe?

Thanks for the reply.. I am still deciding between ca5e and cat6. Cat5e for it's price and cat6 for future proofing. Difference about RM300-400 (cable + keystones, etc).  Any suggestions which should I go for? My main purpose to is to deliver FTTH to all my computers/laptops, file sharing with NAS, and FullHD movie streaming from NAS to network media player.

I am thinking of maximum 6 in a pipe (hub side). They rest are either one or four in a pipe. Is that reasonable?

Edit:

And I forgot to add that I'll be using the network for cat5e/cat6 based HDMI extender and remote repeater.