I dont get the sideboard rules; as I understand it you can only use 1 element and otherwise a total of 6 cardcopies from another element (or your shard) over 5 games, that you even have to have in your sideboard?! or are all the sideboard cards usable a total of 6 cardcopies EACH per match? Even then I feel like certain cards will just autowin several matchups because many elements will only be able to counter them like 2 times which is not enough for a bo5 even if you use that counter perfectly.
You choose 8 cards as your sideboard when signing up.
In each Bo5 match, you can use each sideboard card up to 6 times. (So you basically have all cards in your element an unlimited number of times and 8*6=48 cards you can spread across your 3 to 5 decks)
Also, keep in mind that after each round there will be a list of cards you can choose from to add to your sideboard, so as the event progresses, you can get additional tech cards if needed.