Yes it is smart but it need a good sense of the bitcoin market and proper knowledge about the bitcoin value in the market and the other fiat currencies value in the market, so that you can make your decision what to max and what to not. The maxing is very beneficial but need a good sense
No it is not smart to max out your credit line for anything, let alone a speculative investment
#1 rule of investing is never to invest more than you can afford to lose, if you're investing the banks money via credit then I'm pretty sure you can't afford to lose it and so should not be touching it!
There's a lot of Bitcoin success stories, but there's also a lot of stories about people losing everything in the flash crashes