Hi, welcome to WEC addiction!!
Getting to most parts of the circuit involve one thing, well two actually, your feet! Take good boots and be prepared to walk, its a big circuit and the surrounding roads are pretty well gridlocked during the race weekend. There is a little 'train' thingy that trawls around the main areas of the exterior which you can hop onto and get to the main entrances but these are random, infrequent and usually very full.
If you want to go into Le Mans itself by car best do it on Friday or before, there is a good tram service which runs from inside the circuit if you plan to visit over the race weekend.
Tribune?
We do but its really about how you plan to view the race, mainly moving around or mainly static? Whichever, one of the little tripod style seat things are a minimum requirement IMHO, cheap, lightweight, convenient and available at the circuit. That said, if it rains (and it has been known to

) a tribune seat is a Godsend.
Best advice? Read the Club Arnage Guide, available near here, and don't be afraid to ask.