There is always 4 equipement per event (one of each), no matter the event type. If you've completed the farm events, you should have all the equipements. If you refer to the 6* equipements, it's just the 5* after using Aqua Crystals on them. The wiki's presentation may be a bit confusing.
You can buy them during the event reprint and buy them with no time restriction when the event entrer it's rereprint state.

EX dungeons are a bit harder since last event when it became unlimited but I didn't notice any change other than the nation typing otherwise.
I built two very poweful teams for them so, I just clear everything turn 1. But yeah, it's gets quickly boring to do the same stage over and over when it takes too long.

I'm definitively not cheating by using two Spring Star School
Spring Star School is very good in these stages. I hope you managed to get more than one. Thunberg Spirea Christmas is good too.
Then, good turn 1 with all target skills girls like Dendrobium, Pinkladies Flower Saint, Helianthus, Tritoma obvioulsy... are best choices. And various buffs to make them great. Or stack turn one attackers.
Faster is better here. Girls like Zinnia, Corbett or any other good girls who needs time to setup are not a good choice.