About trains, Marco has it in a nutshell, above. "buying train tickets. I know they can be bought on line, but I don't know if we want to do that before we go, committing to exact times and days. Has anyone just bought as you go?" We buy mainly as we go. The problem with buying far in advance is that the tickets are no good and cannot be refunded or exchanged if you see that you are going to miss the specific date/time your ticket is for. That would mean that that you would have to buy a new ticket, full price, when you are ready to board your train.
It's a matter of how certain you are that you will be traveling on that date, that time. We have bought tickets one or two days before the date of travel; not two months before. That way, the discount is not as substantial, but we are more sure we will be making that train on that day. We have also just bought our tickets at the window an hour before boarding, paying full price. Expensive, yes, but needless to say, we did not miss our train.