How to press avocadoes to make avocado oil

Depends on if you'll buy for instant consumption or for storage.

If you want to eat/prepare them right away, you want an avocado that feels soft on the inside, when pressing them they will cede and have that soft feeling ripe avocado has. It shouldn't cede very much though, as those are past their prime. The very good ones even smell in a nice avocadoey way a bit (or maybe that's just my insanity.)

If you want to prepare them later, you want firm ones that cede only a tiny little bit (the rock hard ones mostly never ripen in my experience,) you then store them in a porous bag (the typical brown paper bag or a newspaper) to let them ripe. To speed up the ripening, you can add an apple to the bag.

See also this related question

This should be no problem. It is basically the same process as making a vinaigrette, only using water instead of vinegar, and lecithin instead of mustard. Here's how I would go about it. Let's say you have 1 cup of oil to emulsify. Go buy soy lecithin at a health food store. Take 1/2 cup of water, and dissolve 1 teaspoon of the soy lecithin in it. Use a blender or immersion blender. With the blender running, slowly drizzle in the cod liver oil. It will emulsify - the oil will disperse into ultra-fine droplets in the water, and presumably the taste will be both diluted and somewhat hidden by being locked up in little droplets. If this doesn't work, you just need more lecithin, so dissolve a bit more in another 1/4 cup of water and drizzle the whole thing back in to the blender.

Naturally you'll want to take 50% more, since the oil is now only 2/3 of the volume.

Those other ingredients are for flavor and anti-oxidation, not needed for the basic thing you are trying to accomplish.