[1]: Approximately.
Everything in moderation. You can often run a single master PostgreSQL system into the millions of transactions a second without having to resort to sharding and other complexities.
Django's ORM is very easy to use, but it is not especially powerful, and when you want to do advanced queries (multiple join conditions for example) it often isn't possible. When someone asks me for some data from the database, usually its easier for me to go directly to the database than use the Django ORM.
Use the ORM to start with, but its most definitely a good idea to learn proper SQL .
So, I think starting with PHP and raw SQL is a good thing for motivated learners.
And if you need motivation, try building a WordPress site with themes and plugins first. And maybe an Android app. And then something cute like a LED blinker with a raspberry.
There's a lot of blog posts on HN about bending databases like Postgres to pretty insane workloads. Heap's workload is a nice example of that. they're interesting blog posts but don't let them distract you. Most databases really do work pretty well by default, if you just use them the simplest way possible. Most apps don't have insane workloads, and especially when you start out they won't.
If you just make a table for every "thing" in your system and link them together with foreign keys you're pretty much set. Most popular frameworks (Rails, Django, etc) do this for you without even touching SQL.
This approach is fine for nearly every case. I bet even Heap started like that. Famously, Twitter started like that as well, and the only reason that got them in trouble (remember the failwhale?) was because they were growing faster than nearly any platform ever before. Most sites don't 10x their user count every half year, and if you do, lucky you. Scaling problems are luxury problems.
Half of HN is jealous of people who have scaling problems. I sure am. The other half, well, they won't have scaling problems because they're not shipping fast enough. Their backends would scale though. They read all the books on Postgres and doing it right from the start!