Might as well actually explain the paths. Both land routes take about the same time, while the sea route is quite a bit faster, meaning you could get to Iron while it's still late winter.
Taking the east route takes you on well-maintained roads through some dwarven settlements, then some human villages as you get closer to Cleft. Turning south you cross the major river with a bridge, then leave the roads for a path. The land is lush and fertile with moisture blown from Skaldivon. You pass by Warped without getting near the magical disturbances, and the path continues hugging the coast between scattered human fishing villages. A heavily wooded area is nearby, fed by a rain basin but devoid of elves, as far as you know. Once you reach the opposite end with the river mouth, you abandon the path entirely and follow the river inland till you hit the waterfall. The land becomes frigid plains chilled with wind blowing from the south.
The West route takes you through more major settlements of humans, and you turn south, cross the river on a bridge and abandon the main road. The land is consists of dry plains created by the rain shadow of the mountains with Morte in them. This area is largely unsettled, and is frequently used by armies north from the frozen wastes, though there isn't any recent activity. You follow the coast down and hit the river.
Going by sea means heading west to a larger human port, and using ships hired by the expedition authorities. They sail closer to the western coastline. The sea is fairly safe, with no known monsters or aquatic races that prey on shipping. The sea is fairly stormy during Winter, however. They drop you off at a small fishing village near the river mouth, on the east side.
The warm water from Iris means that the river is constantly flowing near the glacier, but as it gets further away it eventually freezes in winter. This causes flooding on the tundra south of Iron, creating vast lakes that freeze, melt and reform as the temperatures change. The river north of Iron, which you will be travelling along, will be completely frozen in its southern extents near the cliffs. You can cross it easily, but it will melt in spring. There are some fords along its length, but no bridges at all.