Training Plan for Bike Touring

How many miles per day? Mountains or flatlands? Whats your goal(s)?

Frankly any plan will probably work. I’ve known people get off the couch and ride 500+ mile tours because they ride at a slow pace and not too far each day. Dragging a heavy loaded bike over multiple mountain passes each day is probably slightly different, but why not plug your tour into Plan Builder as a multi day event and choose the appropriate daily time and intensity you expect and see what it spits out.