Currently Joseph is correct. The early high maintenance costs make it impossible to expand much. I'm also on Deity, Eternity game though, and with 8 Cities and 2 techs from Trade I have 167

in City Maintenance. A part of that are from buildings, granted, but it is still way too high.
Your game has not matured enough for the costs to start showing yet, once your cities start growing your maintenance costs will increase too. Had I only had pop 1-4 cities I would have had plenty of

/turn to play around with.
The next highest expence is units with 42

. I like to keep animals around, and I do have some still but am unable to keep as many as I would like. After that it drops to 10

for Civic Upkeep. Just to give some comparisons.
Also forget about warring, the unit cost for doing that would kill my economy completely, even if only defending.
65% science might not be too bad to be able to maintain, with a +1

per turn, but it is when I know that a few more cities growing in pop will reduce that further. I'll survive economically, as long as I don't get involved in a war or do not expand any more.
Oh, and 8 cities isn't much considering I'm playing on a Gigantic map. Later on I might be able to expand more, with the better Civics and better

buildings, but the maintenance costs are stopping any kind of expansionist strategy currently. Have not tried with the Expansionist Trait though I doubt it makes all that difference.
Cheers