As indeed a traditional HN remark, you are giving advice for applications that almost no one will ever need to build because you will never, ever see the type of traffic/users for it.

Also, doing these things ; dejoining, UUIDs and indexing all columns (really unsure about this one; why?), might be better later on, but at the start it will be a lot heavier.

Modern hardware and databases can take an incredible amount of traffic if you use them in the right and natural way without artificial tricks.