Trigger to Update a Field on Account from an Order

I have a field on the standard Order object, this is a formula field and contains text, what I need is when the order is created or updated, to take the value of the field and add it to a multi-select picklist on the related Account of the order. If the Order is Deleted to them Remove the Text from the Multi-select picklist on the Account. I know there are limits to a number of items in a multi-select pick list and not sure how to manage this at this point so I am open to ideas, I am able to after 24 months remove the items that are more than 24 months old but not sure how to do that as part of this, any idea would be helpful. Also if the multi-select pick list is not the best idea, then give me your thoughts as all I need to be able to so segment a list of the accounts by a filter/formula that is simple like contains “text copied from Order”. Open to your thoughts and ideas.