Well the different types of gear will affect your movement speed just as you would think it will, meaning light armor = fast movement speed, studded-armor = a bit slower, heavy-armor = even slower,etc.
If you are going to be wearing robes you will be very agile but keep in mind that your armor rating will be very low. In the beginning you will be an easy kill...but as you level and level perks up you will become very strong. I started playing with leather armor and I have now moved to Elven armor which is one of the lightest armor sets and still gives a good armor rating (for a thief / assassin type character).