Can i make less then the maximum indicated cup size?
In general = Stovetop Espresso Makers are designed and manufactured to produce the best results while using them at their maximum indicated cup size. Meaning that the relationship of the water in the boiler and the ground in the funnel are designed for best results. If you change this relationship by for example using less water or using less grounds, the taste of the espresso will change.
If you prefer to be a little more flexible and preparing less then the maximum indicated cup size without sacrificing or changing the result, you want to look for stovetop espresso makers that have a reducer build in such as the Giannina Espresso Maker from Giannini for example.
However, you will not harm your stovetop espresso maker by making less then the maximum indicated cup size as long as you make sure that you always use a minimum of water in the boiler to prevent the maker from overheating. You should never use less then about half of the maximum amount of water in your stovetop maker. So for example preparing about 3-cups in a 6-cup moka pot is fine but you should not make less then half.
Changing the the relationship between water quantity and espresso grounds is not necessarily bad. It depends on your preference. Some people prefer to actually using the maximum amount of water and only use about half of the grounds to prepare a milder espresso and some do the opposite to increase the strength of their espresso.
What type of espresso or coffee ground should i use?
You can use any brand of espresso or beans you prefer as long as the type of grind works well with stovetop makers or moka pots.
If you grind the beans yourself we recommend a medium-fine to fine setting. If you purchase them pre-ground in a grocery store for example look for the moka pot symbol on the package indicating that the grind works with stovetop makers. The type of grind that works best might also be different for each stovetop makers.
It might make sense to test different ground levels to find the one that leads to best results with your particular model.
can i tamp the ground into the funnel?
In general the answer is no - you should not tamp the grounds but simply fill them into the funnel loosely.
The maximum pressure a stovetop espresso maker or moka pot usually produces is up to boiling water. If you tamp the grounds to firmly into the funnel the pressure might not be high enough to force the water through the grounds and the stovetop maker might at one point give up and start leaking.
There are differences in the amount of pressure the stovetop maker tolerates which mainly depends on the quality of the material and on how well the product is made. If you are using higher quality stovetop espresso makers such as the Giannina Espresso Maker from Giannini for example, they tolerate and withstand more pressure and you are able to compress the grounds more then in other stovetop espresso makers models.
The stovetop maker capable of creating the highest level of pressure is currently the Bacchi Stovetop Espresso Maker that produces up to 9 bar of pressure.