A 90% success rate is very impressive. 50% is more typical.
The 10% won't be a complication rate, it'll be the rate of failures, as in, he couldn't get the baby to turn.
The complications they're worried about are causing problems to the placenta, meaning you have to have a section right away. Because of this, from what I know, you're generally nil by mouth from midnight if you're having an ECV, so if they have to give you a GA, they can.
These problems are very rare, though. And they monitor the baby before, during, and after the ECV, to make sure everything is fine, and to ensure they spot any problems before they become serious, iyswim.
Given that you have had six babies before, that means there's probably a fair bit of space in your uterus, so your baby has lots of room to turn around, even when he's quite big.
Your successful vbs make a vaginal delivery a good option, but only if you can get a midwife or other practitioner who knows how to do breech deliveries. Because of litigation, and the increased popularity of CS, there aren't a lot of midwives out there who have done breech deliveries. But you might be able to find an older midwife who is competant at this?