1 slot only. either melee or ranged, not both. you have to use an action to swap it out. thats what id prefer.
1 slot, if you can't change during combats via inventory is not enough. This would mean an archer can't fire an arrows before going into melee...
On the other hand being able to change in the inventory looks cheesy.
That's why 2 slots is good. It's not too much and it's not too few.
About changing on combats from 1 slot to another, according to me it should cost a bonus action.
