Actually 1 turn = 1 or 2 weeks would be appropriate IMO. But I agree that 2 moves for infantry and 5 for cavalry seems better than 1/2 : this way you can use hit and run tactics with cavalry against infantry. Siege engines should also have less moves than infantry so only 1 move for them would make war tactics way more realistic.
On the other subject you raise, Pef, I think the units should not have such a malus in hills (just no bonus) and only 10% in snow (your opponent also feels the cold), but more importantly those bonus should not apply when actively fortified, since for example it's very easy to fortify a hill against invasion. To represent that, I would suggest doubling the fortify defense bonus in hills and forest (in fine I suppose 50% bonus on hill, 25% in forest as in plains and ~10% in snow would be good at full fortification).
Also lastly there should not be any line of sight in forests IMO, to allow for ambush or surprise attacks.
On the other subject you raise, Pef, I think the units should not have such a malus in hills (just no bonus) and only 10% in snow (your opponent also feels the cold), but more importantly those bonus should not apply when actively fortified, since for example it's very easy to fortify a hill against invasion. To represent that, I would suggest doubling the fortify defense bonus in hills and forest (in fine I suppose 50% bonus on hill, 25% in forest as in plains and ~10% in snow would be good at full fortification).
Also lastly there should not be any line of sight in forests IMO, to allow for ambush or surprise attacks.