1. Usually what is recommended is 6 cm on femurs and 4 cm on the tibias. Espicially if you do both segments at once (NOT RECOMMENDED) But since your starting height is quite tall, you properly could do 7 on the femurs and 5 on the tibias safely. You will discuss this after x-rays usually with your future surgeon. According to Cyborg4life who has done more than 10+ years of experience, researching, talking with patients etc... 6-7 cm on the femurs and 3.5 - 4.5 cm on the tibias is safe and not overlengthening, but if very flexible and have tall starting height, you might be able to do more without overlengthening.
2. I would do femurs first then wait a year, cuz if you rush it, the complication rate is higher and you can usually gain less height. You should wait at least 6 months and ideally 1 year with doing the other segment. Many people who plan to do both segments end up only doing the femurs cuz 3 inches /7.5 cm is more than enough for them. Maybe the same thing will happen to you since 5'11 / 180 cm is not a bad height at all. Femurs also have a lower complication rate, heals faster, and most importantly you can gain more height safely with femurs.
3. Precice 2 is in my opinion what you should use. According to most western surgeons any external fixation is like old tech, and doesn't make sense if you have enough money for internal precice 2, since it's better overall in pretty much every category. Less complication rate, less risk of infection, more comfortable, wide spread usage in the entire world, reverse feature that can save you if you get a non union etc...
Source for this:
http://www.limblengtheningforum.com/index.php?topic=72690.msg223167#msg223167 / and cyborg4life youtube channel espicially his live videos and surgeon interviews.
4. If you constantly think about your height every single day, then this is a sign you should do it in my opinion.