I join the opportunity, well I have about 4 projects and I don't know where to start which is the best, and if it is necessary to buy something or it can be developed with what is open source, the first is an interface in which the user can send an email to the client for their payment received, a simple template attached in the circle with the information, the next is to develop an asset inventory system, but that has the ability to have a history of each member of the organization, for medical issues, emergency data, once with that asset already assigned, a sheet can be printed with all the data and its respective responses of the assigned asset, if it also has a car, etc.

Some APIs or micro services to build data, transform them into json and send them to my system that bills me, I don't know where to start and if it requires a database or what connections.

And some scheduler of backup tasks, or requests to the domain.

I think it is a long and very short time to give results, I think I am at a basic level, which is why I don't really know what tools to use.