@J_ @Bluenote and @DutchGirl thank you for all your comments. They all make sense and I probably stress out too much.
I have to remind myself: 15 years ago I did dare to quite my job with only about 2 years of my expenses saved and no other income and all went fine.
This time: the net rental income is covering with some margin our expenses. On top of that we will have about 7 years of living expenses mid 2020 in cash/invested which we can use to survive for 7 years in case of no income from the rental at all and/or will provide additional income/grow our NW. In about 25 years we are likely to receive social security and some additional pension (something like a 401K). If needed, or because it is fun, we will work either as salary man or entrepreneur now and than to make some side money. And "worst case" we need to adjust some FAT fire wishes or work a bit more here and there. Well, if you look at it that way, we're in a great position, I don't understandwhy I stress myself out so much simetimes

Edit, probably I do know: I always look how to improve things, be more efficient, make more money, have better results. Both in work and private life. It is a bit in my genes as I remeber I already was like this when I was a very small kid. But now I need to learn to look broader and morew with an ERE view and less MMM / FAT FI view. Oh well, never too old to learn.
Thank you again, I will put in serious effort to see if I can get some RE-deal in the coming 3.5 months to be able to make use of very good mortgage conditions. But if not, well than that is fine as well and we'll find other deals, opportunities somehow and enjoy life in the mean time.