Logistics

I don't know if it has anything to do with the number of starbases or not, however it does have to do with the number of ships you can have in a fleet. I don't have the game in front of me, but if you put two ships on the same tile, and click on the ships, it will show you a picture of the two ships in a little screen with a number on it, that is there "logistics value" I guess you could say, different size hulls will have different values, and in the top right section of where the pictures are there is a number and if the logistics value of those two ships combined is less than that number you can put them in a fleet (by pressing the create fleet button, also in the top right corner), which will allow you to go into a battle with more than just the one ship. I hope you understood this, I don't know if I could without seeing it.

You can have as many starbasas as you can aford to build, your logistics value will efect how much they will cost to establish. The only real limitation is your budget.

PS. the price goes up with each new base.

PPS. However you have to have at least 3 grid spaces between each starbase. with the exception of resourse bases.