Well, Sauromatae is tougher, but with the Getai money should not me a major problem. Do it like this...

Turn 1. Move the rightmost starting army towards Kallatis. Insert spy...
Move leftmost army and starting garrison towards Naissos. Built two Komatai and put a Granary, sewer system and roads in the building queue.

Turn 2. Continue moving towards cities.

Turn 3. If the spy did his job. You can now take Kallatis. Leave the archers unit there... Try and keep casualties well down. Besiege Naissos.

Turn 4. If the spy failed to open the gates you can now take Kallatis with siege equipment. Continue Naissos siege. If you consider yourself lucky and a good general try and also take Naissos by storm with siege equipment. Be warned that the garrison there is pretty tough.

Turn 5. Move the army that took Kallatis towards Singidunum.

Turn 6. The Naissos garrison sallies. You take the city. As always try and keep casualties to a minimum. Move a Komatai unit from the capital as garrison. Move towards Sigindunum.

Turn 7. Lay siege to Singidunum. The garrison usually sallies as they have nice troops. Crush them. Leave a unit in garrison duty and move on to Sarmisegetuza.

Take the future capital of the Getai and them finances should be up and running. If you have any troops left better go for Serdike ASAP. It gives you nice regionals that complement your Getai forces...

Hope you like my mini-guide to the first turns of the Getai...