-what is that stage that i'm trying to get up at?
I don't think it's a question of which sleep stage. A sleep stage is a type of sleep. E.g., stage 2 is light sleep, 3 and 4 are deep sleep, and REM is another stage. Sleep stages are repeated in sleep cycles, each taking about 90-100 minutes. Thus, five sleep cycles will take about 7.5-8 hours. The sleep cycles typically go like this:

Cycle 1: 1-2-3-4-3-2-REM.
Cycle 2: 2-3-4-3-2-REM.
Cycle 3: 2-3-2-REM.
Cycle 4: 2-REM.
Cycle 5: 2-REM-1

After the first three sleep cycles you will have satisfied your need for deep sleep, and the remaining cycles consist mostly of REM sleep, so this is the time when you want to wake up. 4.5-5 hours should be about right.

-how do i recognize when i've found the right time to wake up?
If you are waking up at the end of a dream, that's probably the end of a sleep cycle. If the alarm clock wakes you up in the middle of a dream, that's probably close to the end of a sleep cycle.

-if 5 hours is wrong, what do i do to find the right amout of time?
-do i adjust 10 minutes/30 minutes/1 hour/2 hours to do the above?
-how many tries does it usually take to get it right?
I don't really think the exact time is super critical. The main point is that you should have satisfied your need for deep sleep.