What is the best approach to go through levels? Example: Is it better to go through all the levels of FOOD and practice then we jump to ANIMALS and do the same? or we finish level 1 in FOOD and then we finish level 1 in ANIMALS and so on till the end and then we start over for level 2?
How long is a price of string?
It seems something like this is completely up to you. Some people go for crown 5 before moving on. Others go crown 1 in everything first. Then there are people in between.
In my opinion getting crown 1-2 in everything first give you a good base to work from.
Then stengthen your weaker skills, either through checking Duome.eu or focusing on the higher level skills etc
Do you really need crown 5 in “I am a man” “I am an apple” level skills?
It depends on you and your affinity for the particular language in question. One size does not fit all, and one size does not even fit one - as different languages may require different approaches.
A mixture of both, IMO. When we learn something, we immediately begin to forget it. The research on this goes back more than a century and has led to the "spaced repetition" systems that form the basis of Duolingo, Memrise, Anki, etc. The idea is to reinforce what you have learned just before you forget it. I suggest finishing level one in a skill and then moving on to the next skill, while at the same time using the practice button everyday. If you are focused on crowns a way to achieve similar results is to finish skill one and then simultaneously start skill two (towards your first crown) and keep working towards crown two on skill one. Worked for me.