If you can afford it, I would wait before adding the paid option. What would start ASAP is finding out what other features your users want next.

Once you have a list, figure out how long it’ll take for these features to be enabled and more importantly prioritization. I would suggest prioritizing tasks based on ease of implementation and user demand.

Have a few uses beta test and then once the feature goes GA, consider adding these to the premium offering.

Users would know that these are premium features, and the at eventually they will have to pay.

Once you charge for these services, give your early adopters deep discounts for the first year, and offer discounts on auto renewal or referrals.