Sound and Vision
It is often easiest to hire in any specialised AV requirements you may have. Not only will the AV contractor have the latest equipment but they will be used to hire for events and so can advise you about volume levels and contrast ratios.
Most packages are flexible to allow for individual requirements and typically include installation and insurance. You will need to make separate arrangements if you need a technician to attend for the duration of your event, but most will set it up and ensure you are happy with everything before leaving your stand, making provision for glitches and emergencies.