The Novetel is near the port and perfectly ok for a pre cruise one night stay. There are better hotels - it depends on your budget.
You should be able to see the Ship from the hotel.
There are few historic buildings to see in Southampton as the German Airforce flattened it in 1942
The coach is your best means of transport direct from Heathrow or if you want to see a bit of London first, you would get a train from Waterloo station in London to Southampton - they run every hour platform 13/14/15 depends.
Remember that the Titanic made its final voyage from Southampton so do remember to count the lifebelts !!!