To travel from both airports (CDG and ORLY) is quite easy, since the RER B is direct to the meetings venue.
For displacements inside Paris, e.g. from the train stations to the venue, the best is the underground / metro.
Clicking on the link you will find an interactive map with all the underground lines, including the busses network.
Not necessary to say that the best is always to book your stay in Paris weeks ahead !
Please find, downloading the PDF, a list of Hotels close to the venue.