Unfortunately, in group stage there is no clear rule which player should start choosing town Red or Blue. I can only recommend, if anyone is unable to establish it with opponent, that Blue should choose first.
After group stage, in final stage, we will precise the system of castle choosing.
It will be the same like in World Cup (ofc without Necro and Confl). If it is possible, on LH site (admin decide)will be drawing system to decide who starts deleting the castles.