Maybe I should have added the 3 of us are still employed in companies. So we are in a somewhat comfortable position. we are already making a little bit of money

Maybe I should have added the 3 of us are still employed in companies. So we are in a somewhat comfortable position. we are already making a little bit of money that compensate for the administrative and infrastructure costs (which are ridiculously low at the moment). We estimate that the company should earn around 25k € every month so we could quit our jobs but again our costs are very low so far. I'm not sure to properly understand your question here ; you want to have a side business so you can concentrate on your main startup? Anyway, good luck with your business(es)!