a great reading on this topic is Intellekt's post on the following thread:
https://forums.galciv2.com/?forumid=347&aid=131866

scroll down to reply #28

I have to respectfully disagree with your number 4 point on population. Increasing your population above the initial 6 billion will generate more taxes and provide more soldiers for invading enemy worlds - and for defending yours.

I like to build one or two farms per planet above PQ 5 (it's a waste of a tile on 5 or lower because of the PQ pop cap) depending on PQ. There is a 'hidden' morale bonus for planets of PQ 11 and higher, so on planets that will cap out <= PQ 10, I build one farm and one morale building. For PQ 11+ planets I build two of each.

The killer with building two farms is that you don't want to get above 18 billion, which is where morale really starts to tank, so you have to go into the planetary governor and turn off auto upgrades once you have gotten to intensive farming. You may not plan to research advanced farming, but you might accidentally get it when invading someone else.

It's kind of a pain, but the payoff in tax revenue and invasion power makes it worthwhile. I usually do this with all of my colonized planets and any that I capture early on. Once I get to the late period of the game and I'm invading planets constantly, I just try to get a single farm and morale improvement started on new planets to avoid the auto upgrade hassle.

They used to be, in v1.2 and earlier. You could get planets over the "morale" hump and have 100 billion populations - then they nerfed morale and farms   

...and the economy, and now diplomacy is dead, too. This isn't a whine about my favorite strategies going down the tubes. I enjoy changing my strategy and finding new ways to play the game, but I have to agree with you that it seems that alternative strategies are being squeezed out of existence.

Even though I could mod the morale, farms, and econ if I wanted to, the completely gutted diplomacy system is not moddable. I feel as though the game is being slowly manipulated until the only type of game left to play is one of constant military action where all of your neighbors will eventually declare war just because you are the human player. DA kind of reminds me of the Total War series now.

Here is my strategy for a new game on Huge Galaxy on Suicide and with 5-9 other major civs. Note : I always reset the map until I have a good set of stars around me and im not next to the drengin . I also always have pretty much 100% approval through out the game and I get tons of rebel colonies joining up by mid to end game..see it does pay to be good guy

1: Research new propulsion
2: Build colony ships as a fast as possible and send them out and upgrade as propulsions become available
3: send out flag ship to hunt down anomalies as fast as possible
4: Now I use the planet/ship panel to find the highest " unowned" planets in my area and I send my colony ships to the high quality planets right away .
5: At first I am pumping out factories and labs so my colonies get built faster and my research gets done faster.
6: I keep all my colonies at 6billion people until at least mid game ( even the huge class 26 worlds ).
7: I don't even bother building warships I just use diplomacy to keep the potential enemies at bay until I get get my worlds really making money and producing people .
8: I only use econo star bases and usually only along major trade lanes because influence pisses off to many races and military is not that useful .
9: If money starts getting tight build economy tiles . I research to stock markets pretty early on .
10: Go after those alliences and economic treaties it is vastly more profitable to have major tourism on your worlds then you will ever make from trade ships. I usually making 5-6000BC just from tourism alone by the end of the game .
11: By the end of the game I have at least several alliences and when a civ starts getting tough I can usually buy or trade techs to get ships and weapons quickly as I am research them myself .

I usually win by influence or alliences but occasionally I just crush the enemy especially if they start making my colonies defect with influence star bases !

Yeah they said the colony rush is not so important but it seems to me the AI researches techs for colonization pretty quickly and before you know it they are in your back yard . Really sucks when you get a kind of section of the galaxy but half the plants belong to your neighbor which usually set up influence star bases sooner or later . I personally would rather have my complete maybe smaller portion of the galactic pie then share it with a bunch of alien scum ...

So true

I don't know that colony rushing is the only way to start off the game. If you're stuck in the middle of nowhere with no planets in sight, the only way to salvage the game is to build starbases pronto to get to the good planets. Colony rushing won't help you there because the good habitable planets will most likely already be taken.

If you only play the game when you're in the middle of a fat clump of planets, then sure, colony rushing is always the right thing to do.

Games wherein you're "boxed in" or halfway the galaxy to the nearest generally habitable planet isn't unwinnable. It's just a bit more difficult and played somewhat differently.

If you want a change of pace, select for games in which you're placed in a vareity of awkward positions. The game plays radically differently then.

One word that will do wonders to how much you own the AI completely and utterly:
Propulsion.
I can't stress the importance of propulsion technologies enough. It lets you do everything Harder, Better, Faster, Stronger. Obtaining Warp I while still in Colony Frenzy is a game winner in and of itself. Later on, military ships with speeds in excess of 10 will prove a much more effective means of patroling your space, since you don't need a lot of them to cover a large area. Gone are the days of churning out small hulled single-engined planet defenders. One 10+ speed ship per sector is enough, and if one can't fend off an invasion, your improved mobility means that you can muster atleast 3 and at most 8 more ships to defend a given sector within the week.
A word of warning: the Propulsion ability bonus is NOT worth it, too expensive for too little. Those 5/8 points are better spent in Research and Economy, even Military or Social Production.

Playing this game is a bit like going to prison - if you don't kick someone's ass the first day, you'll spend the rest of your time there being someone's bitch.

Basically once you get all the habitable planets around you, and you have all the basic Xeno techs (xeno reserach, xeno entertainment etc) you want to start thinking about invading someone. Researching planetary invasion takes about the same time as researching one of the colonisation techs, and it has the bonus of taking an already fully developed world and stealing tech at the same time. Obviously the best targets are minor civs, because they have a massive homeworld and won't put up much of a fight. Be wary of attacking the Drath or the Alterians because they will often call other civ's to their aid, also I'd avoid getting into early skirmishes with any of the evil races because they usually get powerful much earlier. Good early targets are Terrans, Krynn, Torians, Korx - usually I can invade them before they even have defensive ships.