First install the 995 planets in core sector mod because AI run sectors suck.

Then we get to the actual game.

Take a race with Society research bonus, growth time reduction, nomadic, and weak. Later you will add various traits through gene engineering to each specialized world but these are the critical traits. Take Fanatic Materialistic and Militaristic ethics. Take Desert Preference for planets. Take the Neural Network government that gives research and survey speed. Alternatively you could take the 2 empire leaders and 2 research options government. Later in the game when you have more research you'll take the megacorp government for 10% energy credits and minerals.

Restart until you get a leader with influence. Getting energy credits or growth reduction or corvette cost reduction or mining station cost reduction is a nice bonus. Take the Colony tech and ideally the strategic power generating resource and building from engineering and the 5% research speed boost from physics.

Split your 3 starting vettes up and use them to explore the galaxy. Once you find 5 or 6 alien contacts research them from the situation log. One should be a fallen empire. If its the Enigmatic Observers you hit the jack pot because these idiots will give you ~3000 minerals for a 30 year civilian access and research agreement treaty. That's a massive kickstart to your nation.

You should build up mineral supplies while colonizing all desert worlds 16 and higher and once you get arid and tropical do the same for them.

You should always constantly be on the lookout for a planet with the -33% growth time modifier. Combined with your racial trait and the strategic resource building that gives -15% and potentially other sources this will be the mainstay of your expansion. Max this sucker out in food and habitability. Ideally you want 100% hab. I'm not sure what the ideal pop count is because I don't know if population size has a stronger negative effect than food has a positive effect. Potentially you might want to gene mod the people living here for +food and make sure you have the orbital hydro farms and also top tier ground base hydro farms. Using your nomadic trait plus I think some other stuff I think you can squeeze the influence cost of resettlement really low. This is why you wanted to take militaristic for the influence gain from rivalry and also get an influence leader. You can max out at about 10 influence if you can drop your frontier stations to 0 and have good rivals and all the influence techs. It's too bad there isn't an endgame research tech for influence like there is for borders and such. Anyways with ~20-25 cost for resettlement and 10 influence you are looking at essentially being able to resettle 6 pops a year. That's 60 in 10 years and ~600 in 100 years. I've had empires with less than 600 pop total after 150 years. This is on top of the natural growth of pop on your planets. As we've discussed you can get about - 58% growth time from permanent modifiers. You can also get -25% if you elect the right leader in some governments. So that is a 83% reduction in growth time. I think there may be more ways but I can't say for sure. There is no growth time reduction trait listed in the wiki. Base growth time appears to be 25 with about ~3 extra food per pop? Not sure how that scales. It seems fairly linear from my comparisons. Thus is appears that since you can always gain way more than 3 food per pop using the biggest world you can is ideal. Well, based on my mental calculations the exact numbers don't matter. You can easily generate more population than you have the influence to get rid of. On planets without the modifier or the strategic resource bonus you can get some decent growth but resettlement means that as soon as a planet hits 5 pop you can give it a huge boost. Also because you make more food per pop the extra pop will also boost the natural growth by getting you to the end of the scale faster. Assuming you can build enough structures to keep up. And using proper micro of blocker removal and building boost governors you should easily get ahead during the rush to 5 pop for getting access to resettlement. I would give odds of perhaps a 50% natural boost to pop growth due to resettlement on all planets. I mean you get 35% time reduction from your racial trait and electing the right leader and you still have that 15% bonus for as many planets as you can score the strategic growth boost resource for. I'd say due to how much territory you'll be getting from massive growth you can easily secure that bonus for ~4 worlds not counting your pop farming world. So your growth is going to be pretty damn huge. A normal planet without minmaxing and with good food building placement can probably expect to grow a new pop once every year and a half. You'll be growing a new pop for resettlement 9x times that fast. Your limit here is actually influence and not pop growth. If you could somehow lower the cost of resettlement you could get an even larger pop growth boost.

And yes I am doing this in my current game. OP as fuck.