I would recommend just acouple nights in Southampton, but we used this as a base also to visit Winchester and if we return may even use as base to Stonehenge or Portsmouth.
There is good bus and train service from here.
The questions above do not directly relate to our travels to Southampton. We were there to board the Queen Mary 2 to travel back to the United States.
Access to the port was very easy. The immediate area we were in was located next to Old Town which then accesses quite an active, vibrant shopping area. We may spend time next visit and do some local sightseeing.