title_body: What are the standard espresso parameters (dose, mass/volume, time, etc.)?
upvoted_answer: The question is a very complex one, so I will try to answer with a standard approach of dialing in your espresso. Generally speaking what you should aim for is a espresso that is full bodied, sweet, fruity with crisp acidity, a syrupy mouth feel and an amazing aftertaste that stays with you long after you finished the cup. What you don't want to get are any sour (underextraction), bitter (overextraction), ashy flavors and a hollow aftertaste that leaves you wanting more.
  
  You can get to that sweet spot different ways, using the single shot or double shot portafilter. There are some general guidelines though that you might want to follow.
  
  
  Generally using a double shot porta filter delivers better results. You are more flexibel in adjusting the grind size for example. In basically all specialty coffee shops, double shot baskets are used for making espressos. Surely this has to do with efficiency as well, since you can make 2 shots at the same time. I would suggest you try to find the sweet spot with your combination number 4 (or number 1 if you really don't want any more than a single espresso).
  The first thing you have to consider is your recipe. Using a double shot basket what you should aim for is a dose:yield ratio of around 1:2. That means if you start with 20g of coffee (in the double basket), aim for a 40ml yield (for a double espresso). A very common recipe would be to start with an 18g dose and aim for a 36g yield. That would be a double shot or two single shots. If you pull shorter you will get a ristretto (short espresso) and if you push through more water, it would be a lungo. The yield is not fixed, you may adjust it depending on the coffee and taste. It is just a basis for dialing in properly, a baseline.
  Once you decided on a recipe you should lock in the dose. Changing the dose, changes everything else, so you want to keep it as consistent as possible. However the grams are not fixed and will change all the time. If you change the coffee type/brand/origin/roast etc. you will have to adjust again. Even variables such as temperature, humidity and how much coffee is in the basket above the grind chamber will influence your grinders behavior and therefore the dose. The only definitive remedy is weighing out every single dose and shot (for home use at least whenever you use new coffee to find a setup that delivers consistently good results with this brand or type, albeit it will not consistently be optimal).
  Now that you have the dose and recipe fixed you want to get an extraction time of somewhere between 20 and 30 seconds. Adjust the grind size (keep in mind that your dose changes as well, when you adjust the size, since the grinder measures the time of grinding and not the weight of the coffee) so that you reach the desired extraction time with the given recipe. Don't overdo it though and stay in the espresso grind range.
  Keep in mind that you tamp correctly. Level out the grounds before tamping with slight shaking, hitting the basket on the sides and using your fingers. Try to tamp as straight as possible, the distance between the basket and the edge of the tamper should be equal on all sides. A tilted puck will extract badly. You don't have to tamp terribly hard, just until you don't feel the coffee bed changing any more. Anything more is redundant.
  Pull a shot, taste and reflect if the result is the coffee you want. If it is, good for you, most likely it isn't though and you will have to adjust again.
  If it isn't the coffee you want, try to figure out what's wrong with it. Is it too sour? Probably underextracted. Try to grind slightly finer, so the extraction process takes a few seconds longer to get to the yield you want. Does it taste bitter and hollow? Probably overextraced, in this case do the opposite.
  Forget everything of the above and follow your taste buds! If one or more of those things doesn't produce taste profiles that you like, just kind of ignore them and try something else.
  
  
  This is a general approach of how to dial in your grinder and produce a nice shot. It is not the only one, it is definitely incomplete and it will not be able to replace experimenting and experience.
  
  Also don't bother too much about the pressure at the beginning, try to get consistent results that you like when pulling shots and after a while you will learn and understand your machine better. Also don't forget to flush the group head and portafilter before use, so old coffee oils are removed and you get up to temperature.
  
  Cheers.