Thanks everyone for your input!
We are thinking a lot about buying/adopting two rats. We would love to do "pet rescue", but it actually looks like lots of work. I am also afraid of the emotional aspect of it, as someone said before: getting to love your pet and then giving it away.
We are not rushing into it. We want to think about it before. I am trying to see how easy it would be to find someone to mind the rats when we are away. Do you think it would be nicer for the two rats to stay at our place and only have a visit from a petsitter a few times a week? or to be moved to someone else's house? I thought the second option would be nicer for them, they could play with whoever is minding them, they could see people who would talk to them etc. Not being left alone for 6 weeks... I don't know.