Well, when you will begin play with more AI bidding become more easy... with multiple AI, i usually bid on two AI who don't like each other much... let say 1000 credit on one AI and 1025 credit on the other AI... usually, the second AI wil simply add something like 50 credit on the first one... followed by the first AI adding 50 more to the second... and so on...
These "bidding spirals" are certainly quite useful.
Well, there is numerous tactic possible who can lead to victory and numerous style of play... and pirate in diplomacy are nothing when compare playing against a other human... some can rush you after a few minutes of play, long before the first pirate raid... have only play LAN game... have try ICO 2 or 3 year ago but people was very unfriendly there and i have give up...
Almost forget, if you become bored with single human player game, you will find numerous mod here... a good one for beginner is "Distant star" ( http://forums.sinsofasolarempire.com/335474 ) who add more diversity to the planet type, enhanced battle graphic ( volumetric explosion ) and some balance to the game... later, you can move to races specific mod like Babylon 5 mod, Star War mod, Star Trek mod, Stargate mod, Halo mod, etc... and once you have no more problem with the pirate, there is mod who add several capitalship, starbase,structure to the pirate and make them more difficult
If you get bored with single-player, I highly suggest trying your hand at online games with humans instead. Humans add a much more strategic dimension to the game: although they're harder, humans are much more enjoyable to play with, in my opinion. There's much more tactics and strategy involved.
Though mods are certainly an interesting creative exercise.
Must I colonize lot of planet fast or must I devellop a few of them before ? Where to build what and where to build defense ? I guess intersection point are the best to hold a defense right
Are you developing your planets out of the red? (if you don't develop planets immediately after you colonize, you lose a lot of credits!)
Yes, after accounting for development costs, you should generally be colonizing as fast as possible. Try using the turret and scout trick Darvin described: you should be able to get a new planet at least every 4 minutes, until you have 5 or 6 planets.
It also helps a whole lot if you can research trade ports, and build a few of them in a chain; trade ports increase your credit income rate. If you can do that, then you should be able to support a pretty decent sized fleet by the 30~ minute mark in the game. Build frigate factories on your front line world, build a fleet (composed mainly of LRM or Assailants or Illuminators) and attack the enemy! If you're playing against Easy this should make winning the game relatively quick.
Generally, you shouldn't be researching anything except for the bare essentials (ship types, planet colonization), and you shouldn't be building much of anything on your planets except for extractors, trade ports, and the few necessary military/civilian labs.
If you do this, then it shouldn't be difficult to build a fleet much more massive than the Easy AI and steamroll it.