So, you've brought a starter force. You've played a few games with them and now want to expand. But where do you go?
In the end it's up to you, but the most obvious choice isn't necessarily the best. You might want some big tanks to add more firepower to your army, but is that really going to help? Same with adding more AA units.
What I recommend is to first get your command vehicle, you're going to need one soon anyway so you might as well get it now. This also means your commander is in a proper vehicle with his max sphere of influence.
Next step isn't to get more tanks either. It's to get more infantry. In the several games I've played the lack of boots on the ground has meant claiming objectives can get difficult. This is why I have got some more infantry in Raven light drop ships on the way to grab objectives quicker and give me more objective holders.
Play a couple more games and see what your list is lacking, then get some units to compensate. I've got some Wolverine scout units for additional AA and to help with the Kodiak command vehicles orbital strike as well as some Gladius heavy tanks for additional firepower arriving soon. I'll post those probably on saturday when i should be getting them.