It been awhile since I played a Getai campaign, but I recall it being honestly the most fun campaign ever. I fought every battle myself...do not risk auto calcing battles as you'll need every single soldier you can get (well you can, but you'll be sorry in the long run)

I focused on towns with mines and kept a few spies about for quick city takeovers if they could infiltrate and open the gates. Use plenty of light phalanx. A couple chevrons of exp for them and they are equal to the more expensive heavy phalanx. Try and concentrate on building markets and anything that helps trade like roads. I do recall reaching some crazy debt, so do not freak out (30k iirc) but you'll slowly inch your way out with the battles you win and the towns you take. Once you are out of debt, portions of your army should be well experienced. Once you get the Ischyroi Orditon (Elite Dacian Infantry) you'll rejoice at having your best men to send into battle


This overall scheme worked for me, and it was great once I got out of debt and could really rock and roll with the Getai