If you do not have the budget or possibility to do all of the above, remember that multiple small initiatives make a big difference.
Make sure that every room is accessible to all of the participants, including the audience space, stage, group rooms and dining facilities. Physical access and technical equipment must work equally well throughout the venue so that all of the participants can take part in every part of the programme on equal terms.
Make sure the sound system, microphone and speakers work well. Think in particular about the acoustics when choosing rooms. Make sure there is no echo or background noise. This is a necessity for people with hearing impairments and is good for everybody involved in the event.
Make sure the light system is adequate and that the light in the rooms is adjustable. Make sure there is sufficient light on the speakers. If sign language interpreters are working, the light must be adjustable, so they are visible even when videos are shown or the lighting is dimmed.
Designate a person responsible for safety. Map the emergency exits and assembly points in case of evacuation and fire and find out whether there are other emergency exits for people in wheelchairs. Find out whether it is safe to be on the premises, e.g. for people with impaired vision, and whether contrast marking should be used on stairs, ramps, wiring or other obstacles, e.g., with neon-coloured tape.
Make sure that the entrance is marked with clear signs and accessible by all. Make sure any information tables are low, so everyone can reach them, and that the cloakroom has staff to hang up things or that people can do it themselves, whether in a wheelchair or standing up.