I do whatever I can to justify excluding wizards & sorcerers, first.
Then I look at the setting and theme and work on excluding the obvious choice. For instance, in a game that will involve heavy wilderness exploration/trekking, I drop out rangers and whatever background negates challenges in the wilderness.
For races I tend to stick to the PH but cut or add according to theme. My Ravenloft games, for example, have humans, halflings, and dwarves only for playable races. But my home brew world allows any races at all. Except gnome.
1. What about bards, eldritch knights and arcane tricksters then?
2. Makes sense if the wilderness survival is a thing which is a major challenge in the setting which is obsolete by a ranger just rolling some nature check or taking the kind of wilderness as his favorite terrain.
That is one thing, why I would not allow rangers in a DS scenario easily, the other is how to include them into divine elemental casting somehow which is also not trivial if you want to do this true.
3. Very good decision of those three dwarves are the ones looking most odd to several of Ravenlofts natives, without being seen as monsters.
Skimming through this thread gave me idea.
I own the 4X video game Stellaris, although I haven't played it much. In that game, you create an alien species. You define that species at the beginning with some scales for things like Xenophobia versus Xenophilia (Xenoism?), etc.
It might be interesting to take each of these scales and apply them (perhaps even randomly via a table) to the different people groups, human and non-human, of a campaign. From these profiles, and proximity to each other on a map, you could draw lines and define the relationships and conflicts between them.
Sometimes I wait until the players have chosen their races, other times I will restrict races, it might be as simple as using the PHB races only. In the past I have used the races that weren't chosen as the threat to peace, Dragonborn in one campaign were a hostile empire that had recently been fended off by an alliance of humans, elves, and dwarves. In another campaign, I just asked for no monster races like goblins and orcs since I wanted them to be kept as the bad guys in the campaign.
I haven't really restricted classes yet. I do have an idea for a campaign with no wizards or clerics due to the primitive nature of the campaign, arcane magic hasn't been formalised yet so no wizards and religion is the old religion so the shamans of the tribe are made up of druids instead of clerics. There were probably other class restrictions as well I was going to put into it as well.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.