Remember to keep travel in mind when posting in-character. You don't have to roleplay out every single journey, but you will need a "time gap" in between threads if those threads are in drastically different locations - and you should make note of the time gap in your chronologies so that other players know your character was travelling during that time period (which does open up the option to roleplay, should you wish to, in having characters meet on-the-road or on the same ship, etc.).
Try to take seasonal changes into account as well, since it would take much longer to travel across Thedas in the winter months due to snow and other such inclement weather.
One box equals, on average, 35 miles.
On foot, that means your character will need to set up camp for the night after moving 2 boxes in any direction.
On horseback, your character could probably move 3 to 4 boxes a day in any direction before your mount required a solid rest for the evening.
Carriages and wagons are surprisingly not that fast, travel wise, usually because they're laden with supplies. So, 2 to 3 boxes a day seems reasonable. Something in between travelling on foot vs. travelling on horseback, since mounts pulling carriages and wagons will definitely require rest stops.
Travel by sea, across a lake, or down-river is definitely the fastest. Travel up-river wouldn't be fast, because you'd be going against the current and constantly being pushed back. Depending on the make and quality of your ship or boat, this would cut your regular travel time in half. So, if 2 boxes equals the better part of 1 day, 2 boxes by water route would equal half a day instead.
Redcliffe to Val Royeaux = 2 to 3 weeks (on foot) vs. 1 to 1.5 weeks (on horseback) if you cross through the Heartlands; alternatively, you could shave a day or two off your travel time if you board a ship from Jader or Portsmouth and continue the rest of the way to Val Royeaux from there.
Haven to Skyhold = 2 days (on foot) vs. 1 day (on horseback) - note: this took a little longer than usual since it's through a mountain passage; remember to take the terrain into consideration!
Kinloch Hold to Amaranthine = 4.5 days (on foot) vs. 2 1/4 days (on horseback)
Denerim to South Reach = 2 days (on foot) vs. 1 day (on either horseback or down the Drakon River via small boat)
Denerim to Kirkwall = 1 week
Gwaren to Kirkwall = 2 weeks (this is the route the Hawke's took, after fleeing Lothering)
Seheron to Kirkwall = 3 to 4 weeks (those Qunari in DA:2 meant business)