How does Golos, Tireless Pilgrim interact with double-faced cards?
You can't pick a double-faced card that is a land only on the back

Double-faced cards only count as their front face while not on the battlefield. From the rules on double-faced cards:


  711.4a While a double-faced card is outside the game, in a zone other than the battlefield, or on the battlefield with its front face up, it has only the characteristics of its front face.


You cannot choose Gold-Forge Garrison as your land, as its front face is not a land.

I think you're getting DFC rules mixed up with split cards, which do have the attributes of both halves while they're not being cast:


  708.4 In every zone except the stack, the characteristics of a split card are those of its two halves combined. This is a change from previous rules.


A double-faced card you chose would enter front face up

A double-faced card always enters with its front face up unless it enters “transformed”. If you choose a double-faced card that is a land on its front face, like Westvale Abbey, Golos would not put it onto the battlefield transformed, so you would get the front face.


  711.8 A double-faced card enters the battlefield with its front face up by default. If a spell or ability puts it onto the battlefield “transformed,” it enters the battlefield with its back face up.