For comparison, it takes about four to six months (with medieval to 18th century travel methods) to cross the United States from east to west, though seasonal weather is likely to require stopping over halfway across to start again in late spring. Your two weeks figure, traveling by horse, will be about the size of the state of Georgia (USA). Generally, you can figure hikers will cover between fifteen and twenty miles in a day on a road without excessive elevation changes; riders will do around twice that without changes of horses (with horse changes, they can do much better; Pony Express used to average 200 miles a day with horse changes every few miles) -- mountains will roughly halve those figures, or worse, depending on how good the roads are.
The biggest thing affected by the size of the land is how many people can live there -- there are many reference available for medieval population densities and carrying capacity.
And the continent is an island. There might be other countries further away, but so far the part i've drawn up is the only thing i've planned
– DM Chris Jun 22 '15 at 18:39