Three spells or one spell slot

so i have a fps game with slots which player can use spells, if it is going to be a three spell slot, i worry player will use less of their guns. but if i use one spell slot, i worry there wont be much varity and builds. what do you guys think?

1 spell slot. Having 3 will make it so there’s less penalty for choosing a spell, so having a single spell slot would encourage builds.

i think i want to have three catagorys, offensive, defensive and buffs…? and having three slots will ake the player ony choose one per catagory, not sure that changes anything hough.

Make there be three spells the player can have equipped at a time, but have there be only one slot, and then have the player shuffle through them, like if they pressed F it would change to the next one.