'91 Legacy is not an interferance motor, if the T-belt brakes it will not damage the engine. It will however be very inconveniant for you.
The T-belt cover is a three piece cover; left, middle, and right. To just inspect the belt you can remove either of the end cover pieces (left or right) and expose the belt. I would not replace the Water Pump unless it has started weeping Coolant or is noisey.