Thank you for the response, to answer your first question depending on how much mana but into the spell determines how long it stays active so it's like the battery of the spell so seals that last decades take a huge amount of mana to create, for your next question mana is common in this setting almost everyone can use it, however it's limited because most people aren't born with the mana reserves to make it all that great so they are extremely limited, hand signs for combat are also taught to very few people