#Downtime rules for running a business are the best official option right now
Downtime rules for running a business are the best official option right now
Effectively, what you are trying to do is run a pirating business. Luckily, in chapter 7 of the DMG there are rules for using downtime to run a business.
Running a Business Adventurers can end up owning businesses that have nothing to do with delving into dungeons or saving the world. A character might inherit a smithy, or the party might be given a parcel of farmland or a tavern as a reward. If they hold on to the business, they might feel obliged to spend time between adventures maintaining the venture and making sure it runs smoothly.
A character rolls percentile dice and adds the number of days spent on this downtime activity (maximum 30), then compares the total to the Running a Business table to determine what happens.
There follows a table which contains various results that might occur from running a business. This is a highly simplified system and it combines profits, costs and other such concerns into one simple roll and one resulting number of money earned (or lost).
###These are simple rules, but you can use them as a base to homebrew if they are not what you want
These are simple rules, but you can use them as a base to homebrew if they are not what you want
This may not be as in depth as you want, but it might be more fun depending on the group. Not every group likes dealing with number-crunching to the extent that calculating actual costs and profits might entail.
For better or for worse, 5e doesn't contain any rules for such a detailed system anyways as part of its design ethos of simplification.
So, if you really want to go the more detailed route, you are going to have to create/modify your own rules to support that. That being said, the rules above should at least give you a place to start even if they don't fit perfectly.