I agree with most people on here in that your arms really are short, no joke.
If you end up doing 20cms altogether then you can bet your left nut you'll end up looking like a penguin in stilettos
Heck you may even walk like one... I live smack bang in the middle of my city and its party central all night, every night and I see so many girls with small torsos walking around in 10-15cm heels, perhaps even more and they look so damn funny when they walk. Looks too unnatural
No point being that tall if you'll just end up looking abnormally weird, yes you can possibly hide it by dressing accordingly but even then it will still be a little off.
I understand you want to save money and are trying to come up with excuses to do 10cm tibias in one sitting but thats just unsafe, I too would like to save money and go crazy in one sitting but I wont, its simply too risky and you're pretty much gambling with your health. There's no price when it comes to health. Like a previous poster already said, if you dont have enough time and money to do 2 surgeries then too bad, do one
TL:DR - You will be the circus act if you go the full 20cms, guaranteed or your money back. You can put your mortgage on that
Arms are simply not long enough, perhaps maybe if you decide to lengthen your arms as well. I know you said you dont care about your arm length but arm length
WILL become a problem
Good luck though