You decide that too! I recommend sticking to simple readings with 1–5 cards, rather than more complex readings.
However, if you are keen to practice your skills and want to do 10+ card readings, go right ahead. Be sure to make managing your energy and time a priority.
In terms of writing up or recording your readings — that is also up to you. There is no minimum or maximum word count. We have some readers who submit one short paragraph per card drawn, and readers that submit 2 or 3 page PDF reports with lots of detail. It’s completely up to you, and your own reading style.