Welcome Mick! Every one is different, but the amount of lengthening you're aiming for is at a safe range.
I wouldn't recommend doing all four segments during one operation. It can and has been done, but it adds unnecessary risk of death by fat embolism; physical trauma, i.e. the surgery, triggers fat to clog your arteries. You can minimize this risk by staggering the two procedures, at least by a couple weeks.
If money is not a problem, choose an internal lengthening device like the
Precise. It's costly, but it's state-of-the-art for CLL, not only by technology but also comfort. If you want to save some money, opt for externals on your tibias; I personally gravitate toward hexapod fixators as they are well-suited for correction if necessary.
As for doctors, you'll want to read through the forums and decide yourself. Make a list of your must-haves, find doctors that fit those needs, and start asking about specifics. In general, the doctors in the U.S. are at the top of their game, but they're also the most expensive, though a portion of it can be covered by health insurance.