Get someone on the field to help you mix the sound. The style of chosen music will affect how you play. The P.A. also has the advantage of being able to be used for the party on Saturday night. It gives you somewhere to store food, have massages, etc. out of the sun. Make sure it is well pegged and staked.
Wind can play havoc with poorly pitched marquees.
You will need at least one person to be permanently at the rego table and who is not playing. Remember, they have to handle late arrivals, media, photos, recording scores, time caps, defusing bombs, delivering babies, not to mention drinking all the beer in the eskies. Basically it's a full time job. Food Try to make sure there is always food and drink available. Making rolls takes a long time, but is good karma.