Absolutely. I do batches of a quarter to a half usually, but 3 grams will work just fine.
.3-.5 is usually sufficient, but you do need to try different doses to find your sweet spot. There are factors other than tolerance, like metabolism for instance. I know people who get high off .1 and completely destroyed by .2.
If you're going to cook it into food, just use as much oil as the recipe would call for (as long as it completely covers the weed/hash). If you're taking caps, what I do is count eye dropper's worth of oil, as one full eye dropper is approximately equal to a 00 cap. So for instance if I want my caps to be around .3 g each and I start with a half, I do ~45 drops. It doesn't work out exactly but you'll be close. The lower the quantity the harder it is to get the caps at a high dosage with herb, so you may have to shoot for half a dose per cap, but taking two caps is not a problem. When you use hash, it takes much less oil to cover so higher dose caps are easier to make.
Something to keep in mind: When you take caps, there's no food involved to trigger digestion like there is with a proper edible. Taking them on an empty stomach is preferable but immediately eating a fatty and/or carb rich snack speeds up the process. This depends on individual metabolism, though. Some people do better skipping this step.
The argument isn't whether it works, it's whether it's efficient. If you don't care about wasting weed and money, by all means take the short cuts. Despite what greenthumb says, I've never said they don't work. They do. They're just wasteful.
In my experience VG is a horrible solvent for cannabis and I assumed PG was similar. Maybe I'm wrong. But the amount of marijuana infused VG needed to actually get high wouldn't fit in even the largest vape tank. It just doesn't hold enough per volume. If you have direct experience with doing PG extractions, I am very interested. If it's substantially different than VG I'll want to start experimenting with it myself!