> All this doesn't mean your back-end should be based on something like Microsoft Windows Server with MS Sql Server.
Why the hell not?
From a technology perspective (i.e., data/information theory/performance/what HN should be about), MSSQL is really, really hard to beat in a big enterprise ecosystem. This isn't because of decades of prerequisite evil dealings that make it a morally incompatible offering, but because it's been so thoroughly exposed to every possible use case that yours would certainly flow nicely.
I've been watching a lot of otherwise really compelling ideas and high energy teams get turned into complete shit due to these ideologies. I can understand a EU tech startup being hesitant toward US-based technology, but in 99% of the cases I hear about, it's a purely American tech company with zero international presence that is making a bunch of noise about how much they hate whatever domestic/paid/"closed" offerings.