but you should not be afraid to continue expansion because of maintenance.
Hmmm. I think you're underestimating the severity of the colonial expenses. It is 325 BC, I have four cities on my home "continent" (there is no more food, not even for sharing), four colonies. My most advanced tech is Construction, I am more advanced than any of the known AIs.
Before founding the 4th colony, my GPT was +34 on 100% tax and -54 on 100% research. After founding the fourth city this changes to +19 and -76, respectively. This means I go from ~3 turns of saving money for every ~2 turns of 100% research to having to save up ~4 turns for every ~1 turn of 100% research. The research output at 100% is virtually the same, 102 with 4 vs 109 with 3 colonies.
This means my research slows down from ~200 beakers every 5 turns to ~100 beakers every 5 turns!
That's half. I don't see a way to continue the game with this limitation, I could barely maintain my lead in tech before, no chance to do that now. I might add that the 3rd colony already slowed me down considerably. Building another, 5th colony would totally cripple my research, as every colony gets increased maintenance when you build another one.
Colonial expenses have increased from between 7.58 and 9.91 to between 10.94 and and 12.68.
I will upload that game tomorrow - should I to it one save / screenshot for 10 turns at a time and let you comment or do you prefer me to upload the first 100 turns all at once?