I have just started to get my monthly income from my apartment. It seems that there is some tasks I have to do. Is everybody working with a lawyer for this?
Did a lawyer or real estate agent help you review the lease that brought in the monthly income? I would ask them what tasks.
To issue receipts for rental income received (on Portal das Finanças I think), it seems plenty of people do it themselves without having to pay lawyers or tax representatives—you can Google or search on this forum for the exact steps.
You better work with a solicitor or a lawyer at least for the first year and learn the tasks. You should be able to use the portal das finanças for some tasks such as to submit your contract, issue the monthly receipts and file annual tax returns for IMI and rental income as far as i know. But i am not an expert, these are not the type of of tasks to learn from internet. you better talk to a lawyer or a solicitor.