SSD as cheap RAM... RAM from the late 70's early 80's... with a short lifespan. SSDs are GREAT for ROMs but extremely active data will murder them.
"It’s not necessary to build a scalable architecture from the start."
This is a BAD idea from personal experience, unless you're a kid with rich backers who don't care about redundant work and fast upfront results.
"Treat nonlogged in users as second class citizens."
Pretty dick thing to do since that's where most ad rev comes from, although Reddit can't even serve it's registered users, shit overloads on peak all the time, they're raking in cash and don't want to invest it in better hosting.