Going anywhere where EV couldn't reach would most often require some sort of reservations; hotels, skiing resorts, museums, sight seeing etc all require some sort of planning if you don't want to absolutely burn money buying things ad-hoc, which would go counter the point of saving money with an ICE anyway.
A month or two in advance is just fine, most people can do as much. They do know how many days of vacation they get though, and it's unlikely to change, so any plan you have you keep.
A month or two in advance is just fine, most people can do as much. They do know how many days of vacation they get though, and it's unlikely to change, so any plan you have you keep.