I don't think too many settings should be changed from standard, since part of the purpose of the ALCs is to make some sort of comparison between leaders possible. 3.13 will probably provide enough of a change to the AI compared to the Isabella games, so I'd steer clear of aggressive-AI this time out and see how the new Emperor copes.
Gilgamesh is a nicely balanced leader. Ziggurat's coming with Priesthood rather than CoL is a big bonus in the early to mid game, beacuse it gets you:
- Early courthouses.
- REX-ability (creative plus low maintenance cities early on).
- A head-start on EP against your rival(s).
- More freedom in early research priorities.
In this case, the creative trait and the UB work very nicely together because you can keep spreading much longer than you would otherwise do during the initial expansion phase of the game (map-permitting).
Not needing CoL for courthouses also allows you to pursue other techs. Given the tweaks made to the AI in BtS compared to Warlords, my favoured approach with Gilgamesh has been to tech to priesthood, chop the oracle and grab monarchy with it since this can give you a real headstart in city growth vs the AI - something you can really leverage rather than waiting for them to research it and be willing to trade (in which case you'll always be playing catchup in that regard until the war machine takes over).
Population = Power and with the UB unlocked you'll be able to afford more, bigger cities early in the game, which has to be a good thing.
In terms of tech, not needing CoL as early leaves you free to pursue other techs such as calendar and aesthetics/literature, which gives you a shot at some useful wonders and can increase the availability of health and happy into the bargain.
Ironically, I think the main problem with Sumeria is the Vulture being such an early UU because you're so well set up to REX (imperialistic rather than protective would be complete overkill). This leaves us praying for a non-Babylonian/Malinese neighbour to take out in the early game, in which case I'd save all the cities you take (free settlers) and use rapid access to the UB to dig yourself out of the financial mire. In many of the ALC games, you raze cities to refound on the perfectly dot-mapped location hundreds of years later. My gut feeling is that you'll gain more benefit from keeping a city in a slightly suboptimal location and having it available sooner, especially with the Ziggurat to lighten the cost.
Long-term goals are really map dependent and probably not worth dwelling on here since UU and UB are so early on the tech tree.