I have my surgery set up with Dr. Lee and here is what I can say from my consultation/research:
The surgery is heavily dependent which Surgeon you go to and I don't know anything about international center for LL to give an insight about them.
1). Complications - the most common is probably infections and delayed union ( they can be treated if caught fairly early - but reading from this forum some Surgeons will actively deny it as they don't want to be accountabile ). The most severe complication is probably death from PE; however, the chance of dying or even getting serious complications is extremely low especially if you go to a LL Surgeon that specialize in these type of surgeries + have a dedicated in-house team ( I am saying this because lot of hospitals will outsource critical post-op treatments such as PT).
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Lot of complication come from some Surgeons recommending crazy lengths + rate of lengthening ( usually it's .75mm - 1.0mm, but there are instances of Surgeons pushing patients to do 1.5mm - 2.0mm ).
2). Can't answer this myself, but there are lot of blogs floating out there especially in the Japanese twitter space ( hundreds of them go to LLT and do crazy numbers like 12cm+, but they seem to be satisified and flexible enough to dance/walk ). This guy (also a Doctor ) is a very famous Japanese LLer that did 10cm I think 4-5 years ago:
3). You are 18 and relatively young so I would forget about the surgery for now. It can cost 80k+ for a competent Surgeon and, unless you are from a rich family, that money can put you in debt for life ( especially if you get a personal debt - those usually have extremely high interest rates ). I would honestly say just get a good job, bust your ass in your early 20s, , save up, and look into it again in your mid 20s.