I have some ideas!
Make the Tau'ri (Earth) have several different kinds of SG teams.
For example:
Engineering Team, 2,2,1 able to build cities (bases) and do worker actions, unable to attack bases, costs no population to build.
This team should cost alot to make up for no population cost. Maybe you should make the humans unable to build "aquaducts" and instead have a small wonder that makes Stargate Command able to grow beyond town size. In the series the humans never had anything larger than small outposts and my idea makes sure that only Stargate Command is really productive. Actually i think that the cities should only be used to get a resource or a valuable bonus resource (I'll get to that later).
Science Team,0,0,1,Able to build colonies.
This team should be a cheap and temporary way of getting resources.
Explorer Team, 8,8,1, unable to attack bases.
This should be the humans first unit. It's tough enough to take on any dangers that might be on the different planets (Monsters, crystal entities, nanobots, viral lifeforms etc.) but unable to conquer the natives (There should be natives on alot of planets) due to it's inability to attack cities. (The humans aren't warmongers!) The Explorer Team should upgrade to Combat team.
Combat Team, 12,12,1, able to take bases.
The upgrade from explorer to combat team represents the human transition from peaceful explorers to a force that openly fights the Goa'Uld. It should be able to take on several Jaffa teams on it's own. The cost should also be high to keep the numbers low.
Government ideas for the humans:
Military Control: This should be the first government for the humans.All units is free under this government. It is required for human barracks construction (Veterans should have 6 hits and regulars only 3). NO corruption in this government. Draft rate is 0.
Civillian Control: This is a "what if" government. It should first be accesible late in the tech tree. Unit costs is massive in this government but it allows for a number of free ones per city. It should get the commerce bonus and be required for the Civil Disclosure small wonder. This wonder should allow all your small outposts to grow beyond town size (Represents immigration to the other planets). This makes this government an absolute must for making a intergalactic human civilization but it's weak units (no barracks) makes it impractical when still fighting a war against the Goa'Uld. No corruption is experienced. Draft rate is 1.
Tech Ideas:
The humans should have some "trade techs" they can sell to the natives. None should be able to research them and they can only be aquired from the humans.
Medicine: No desease, allows hospitals (or something)...
Advanced agriculture (Some natives and Goa'Ulds should start with this): Allows irrigation.
Advanced manufacturing techniques: Factory
And other things like that...
Human Wonder ideas:
Finding Ancient Antarctica Base: Required for Pegasus Expedition.
Pegasus Expedition: Required for Pegasus Expedition Rescue.
Pegasus Expedition Rescue: Require ZPM resource. This is a rare resource that only exists a few places (On a heavily fortified Goa'Uld throne world for example). You bring back ancient technology. You win the game.
Small Disclosure: Disclosure for the major Earth nations. 100% production bonus and +1 commerce in all squares.
That's it for the human ideas. Now for the Goa'Uld ones!
Unit Ideas:
Jaffa Warriors 6,4,1
Cheap dispensable warriors for massive swarming.
Elite Jaffas 7,8,1
Expensive warriors for defense but too costly for large attacks.
Goa'Uld 2,1,1, Hidden nationality, invisible, detect invisible.
Useful for spying and counterspying. Should be costly.
False God (Anubis, Aphophis, Chronos etc.) 1,1,1.
King unit. You lose if you die.