Huge map, 6 opponents. I grabbed 11 colonies (very hard to do, as I had taken malus on any ship traits, and that hurt me during colony rush, as my colony ships had a speed of 2, with a range of 16 because I was bulky (+30% mass) ).
Yes, factories would have done much better. On the same planet, I can pump out 2x more culture with culture fest and all factories, vs all the highest tech level culture buildings (I used Anterian tech tree as well), and 2 factories on culture fest.
A bigger map just means a bigger pain. You will have more planets, but so will they. I set up my games where most stars have a habitable planet. Anything else I think is silly, playing on huge insane maps, where only 25% or 50% have colonizable planets. It just makes the game take longer...and more micro. I like to micro, but micro on that massive scale is not appealing to me.
In all honesty, you will find a tech rush will be much faster. If playing defense, make a B-line towards planetary defense dome. They are so OP The AI invaded several times, on several planets, and just...died, and I took 0 causualties. Until then, grab as much Elurium as you can and make Elurium Defense Shields, before the 50 turn trade expires (or they DOW you). Without Elurium or Defense Domes, its tough. With a prep center, planetary defense shields (adjacent to colony capital), and military academy beside each other, you can get a 65% Planetary Defense, with the other tech bonuses as well. If you are playing a militant race, you may have other military adj bonus buildings which can help. On one planet, I had to install Hyperion buildings, just to get a few more +1s...but it was worth it as they focused on that one planet.
I had a 185% Resistance on top, so 3.0 troops against 12.0 pop with 75% resistance, I would lose maybe 1-2 pop, which hurt. The AI continued to try, but my birth subsidies were barely keeping up with losses. A human player would have sent more troops to secure the victory (albiet take HUGE loses himself). And make sure to get the enemy's WMD counter. I only got 1, and it looks like the 2 remaining races have BIO warfare, which I didnt get the counter. But, my diplo is so high, they are ignoring me, just fighting themselves, hahaha.