Cash flow is definitely a problem that has been noted in other threads, but I have not seen a solution yet. As a work-around, I routinely create the primitive bowmen and immediately cash them in. However, the AI's don't catch on to this trick and most stay financially weak, at least in the early game.

I too experienced this issue, and I built the warrior (15 per) as the workaround. I was able to maintain a positive cashflow. However, there are tons of other balance issues. Early on, the Spanish Natural Wonder doubling is formiddable, and the production bonus allowed me to wage a war of attrition against my neighbors with that early melee unit that has no maintenance. The science bonus meant I was in the medieval age by around 1000 BC. I'm sure I'd find similar blind spots in the other civs, but until this kind of stuff is cleaned up, I'll be dropping this one off.

BTW - I was playing at Epic pace, huge map, and on level 7.

My workaround for this issue was to send out four or five units that did nothing but hunt down barbarian camps. On a Huge Marathon game, this worked very well. I'm not sure if it would be as effective in other scenarios.

Between this issue and the severe resource clustering of the Middle-Earth map mod, though, the computer players fell so far behind me in the early game that it became a joke. Even with just a party of six basic warriors and archers, I was able to start taking cities. As upgrades came along, I started wiping out cities like a plague. I'll be curious to see how it plays on a more normal map, but I'm gonna play the "joke" for a while yet, just to say I've played a game where I razed every other player's cities except their capitals.

I edited the mod and playing Marathon, Inmortal, YnAEMP real starting positions, 22 civs and AI's use to do a solid start, around 8 AI get to Ancient era before than me, as much as 40 turns before than me! and that's playing as Japan, where I don't need to bother to build military, just grow and got Mt.Fuji as huge boost (3 culture 3 faith 2 gold).
Sure the mod is unfinished but with some tweaks is still really enjoyable and balanced enough.