Play around with a gear calculator, but you can probably push a marginally taller gear with thinner tires and lighter rims, so maybe try 42x15. As for brand, if you can buy local get whatever name brand is around (EAI, Dura Ace, Surly, whatever), if you have to buy online dura ace is great and cheap, rockwerks is rebadged surly and are also perfectly fine.

I'm not sure what you mean by "spacing the tires." As for the freewheel size, if you want to use it to bail out on hilly terrain I would go with a 1 or 2 tooth larger freewheel, that way you can climb up in a little lower gear and then coast down. Those of us who live somewhere flatter usually go with the same gearing.