No tickets required. Bring a warm blanket for Friday night freestyles as it can be chilly. You can also bring snacks / wine 
Cheapest hotel options will be at Palm Beach airport, or look for an Airbnb in the Lake Worth area. There is very little inventory in Wellington during the season and prices are high.
Thursdays are the best day for watching dressage during the day as you get the Grand Prix qualifiers for both the special and the freestyle.
Food and drink options at global are really limited so you may want to bring your own.
Saturday go to jumperland for Saturday night lights. Worth it for all the shopping alone