Newb needs help with event wifi setup

Hi reddit community! I'm on the board of a small nonprofit that has an event coming up in a rural area with very limited cell service. We would like our ~100 event attendees to be able to stay connected to a wifi network. Our conference takes place in three different buildings in a small downtown area (about 2 blocks) with a large outdoor lot behind. Each building has its own wired connection. I'm thinking I can put one or two AP's in each building (connected to modem and outlet in each respective building) and use the controller software to set it up so that network id and password are the same everywhere users go. I'm also thinking of putting up a Unifi base station XG mounted outside at the end of the block, facing down toward the other end, to provide some outdoor connection. Any advice, preferably avoiding jargon, is much appreciated. Also recommendations for which products are best suited for this task. Obviously I'm not a networking professional but I'm capable of following directions and have a basic understanding of how computers and internet devices work. Thank you!