well you know, its purpose is: you have the battery on the motor of your RC vehicle. with this so called BEC your able to power your receiver and servos. and dont know the data but its usually around 2A, 5V.
That's roughly correct. It can be as high as 3A for some BECs. You need to consult your ESC manual for the specs on the BEC.
You are aware that you need to use the SERVO library to drive the ESC ?
(i dont want to use the LiPo directly because the voltage may drop under 7V
Clearly you have no experience with Lipo batteries.
Each cell must NOT drop below 3.2V/PER CELL.
A 3S LIPO has a nominal voltage of 11.1 volts and a fully charged voltage of 12.54V.
AT NO TIME COULD THE VOLTAGE ACROSS THIS BATTERY DROP BELOW 9.6V without PERMANENT DAMAGE to the battery AND THE RISK OF FIRE !
If you were using a 2S LIPO, which has a nominal voltage of 7.4V and a fully charged voltage of 8.4V,
your concern about the battery voltage dropping below 7V would be valid, because a 2S can be discharged down to (2 x 3.2V/per cell) = 6.4V.
However, in your post you state you plan to use a 3S (11.1V) LIPO, so your concern is only valid if you plan to DESTROY your battery and start a fire when it spontaneously igninites because you discharged it below the rated 3.2V per cell.
DO YOU PLAN TO DESTROY YOUR BATTERY ?