The XP spent on ritualism skills does not count towards your ritualism level, and hence does not count towards the limit per event spent on ritualism.
2XP in to ritualism would make the character a first level ritualist – allowing them to contribute to one ritual per day, but not lead any separate ritual.
Spending 3xp on alchemist would allow tbem to lead two extra potion rituals per day, and whilst leading them they would effectively be a lvl2 ritualist
Net effect – the a character above can create 2 potions per day, as if they were a lvl2 ritualist, and contribute 1 level of ritualism to someone else’s ritual once per day.
As they are independent the XP on ritualism skills does not affect the 5xp limit, so a start up character could spend 8 xp (5 in to ritualism, 3 in to alchemy) – making them a Lvl2 ritualist, able to lead one ritual of any type, contribute to two other rituals, and lead 2 extra potion rituals at an effective ritualst level of 3.