I am open to all the options. I only do not know which one is the most convenient. In some countries you need to pay taxes in the place where you are working
I got tired of the high taxes charged to small companies around here. Last year alone we got royally charged over 65% of the income for no good reason in DE. With a stable customer base, it has been good (less taxes, less hassle) to work from PT.
My tip is that you also look on other cities besides Lisbon.
On our case we moved into Coimbra. It is directly on the middle way between Porto and Lisbon, between 2~3 hours away from both airports using public transportation (trains/bus have Wifi). Airplanes tickets are costing ~30 GBP for a back and forth trip between PT and Frankfurt through RyanAir.
Housing prices in Coimbra are amazing, I'm renting a full house with 5 bedrooms for ~240 GBP/month. This is an academic city similar to Edinburgh, about 2000 years old with roman buildings still around. All that to say that we get the good stuff without that metropolis pricing of a big city.
Just don't drive a car around here, I have the impression that turning blinkers are not default equipment on these cars.