It all depends, naturally. If you state wood stain, which you do, the implication is you are interested only in giving a color and finish effect, mat or glossy. Straight pine tar will do that. To alter the color it is a simple matter of adding pigment. When you start with additions like linseed oil, turpentine and stuff like that then you are expanding the nature of your treatment to things like added protection, penetrability, application modification.
So what do you want and what will be the status when you and done, might be two basic considerations at the outset.
This Stockholm tar, linseed oil, turpentine is known as roslag and is typically a covering for roof coverings.
Greetings,
Don