On the old forum, everyone used to talk of doing 10+cm by doing 7-8 in each segment. What people quickly learned is that this caused a very long multiyear recovery with large losses of mobility and perhaps permanent leg pains.
Now, the "smartest" decision is to do 5cm in tibia, and 5cm in femurs. You could go up to 7 in femurs perhaps, but for tibias it's not recommended to go past 5. It depends on whether you're willing to do 2 surgeries, or perhaps you want to just get 7 from femur (because there is a risk of permanent knee pain when you do Tobias).
You can do this in the US or the EU with your tried and true options being Paley and Guichet respectively. Paley has an entire institute dedicated to limb lengthening and is by far biggest sorry living. Guichet is also well regarded and places lots of emphasis on ore training and atheletic recovery. Guichet is much cheaper, if memory serves correctly, but I highly suggest going with Paley as his patients, from the diaries I've read, have the shortest recoveries and I feel like for an American WPB is a very nice, warm location to recover in.
My two favorite journals so far have been Iamready and DoingItForMe. They both did what I would call very "smart" lengthening journeys and both showed really good results. I feel like the 5+5 framework will continue to be followed and it really is your best bet for best mobility and recovery time.
I'm sure someone will answer the other questions, but if not, I'll come back and pick them up. I'm 5'4 as well lol so I understand. I think 4 inches may just be better for our size in terms of proportion, I have the frame and torso of a 5'4 person and I feel like even if I were to do 4 inches and work out extensively I will look slightly narrow. But that's just my body type.
Welcome to the world of LL!