My concern is why waste the time, energy, and money to lay brass or any other substitute, and then change to aluminum later? Since you think your going to go battery already, why not lay aluminum down the first time, deal with the limitations it has as a track power while you are converting your fleet? Or do as many others have, set up a trail car system so that you can run multiple locomotives and only have to convert 1 to battery at the start?
As for track I’d go with code 215 aluminum, and handlay. But that’s my choice.
Craig