1. The only way is to try it - the amount of output the simulation produces is only indicative of how radical the upgrade will be. Be prepared for failures - to minimise burning 'coasters' burn to CD-RW or run the iso image in e.g. VMware Player if you have it.

2. The ways in which the system could 'break' are so open ended that I couldn't predict, nor, probably, advise a fix for them. The cleanest way is to forestall, rather than 'patch', a failure

... but be not downhearted . If you update your /etc/apt/sources.list file as advised here
http://www.knoppix.net/forum/viewtopic.php?t=27800
you are very unlikely to have problems.