I should be a tour guide 
First Stanstead – It is a little bit of a way from Hammersmith so what ever you do do not get a taxi it will destroy you! I would get the stanstead express into Liverpool St which is pretty fast and very often – Then looking at the map easiest route is probably Central line to Holborn where you can get on the picadilly line to Hammersmith Or just get a taxi from Liverpool st
Re hotels – Give Margaret a call who is on the hotel page of the website – Her company is a hotel and venue finder so she may find you a good deal or TBH I always find the best deals online – Dom is always good at finding them as well – Use the usual websites for that