Best way to safely host a high volume online transactional wallet?
It seems to be a good approach. The fundamental is keep a little bit "hot" to high liquidity and keep the rest into USB stickers + papers and if possible keep it safe in a vault or bank. Also, keep the anonymity and security of who has the access to the Bitcoins. Remember: Bitcoin is real money, and if you are working with a lot of money, it can be dangerous, someone can try to extort you to reveal all secret.

Don't forget too that USB stickers are volatile in long term by definition, and are not 100% safe. CD and DVD can scratch or can degrade over time. So, the paper is fundamental; keep it in a clean and dry place. Remember also to generate the wallet keys in a offline computer (installed from zero if possible). Read this article: How to set up a secure offline savings wallet.



There is a nice article about it here: Coinbase now storing 87% of customer funds offline