Re: Is it easy to bump other strings?
I'm going through Greg's book, which is written for a 10-string, so for now I tend to ignore the 6th and 12th strings, although the 6th string has been very useful as a "buffer zone" between melody and bass. Obviously I intend to explore the use of those 2 extra strings as I get better at this...
The basic technique is the same whether you learn on 10 or 12 string. I think the basic chord, interval and scale shapes are easier to see on 5 strings than on 6.
I would encourage you to get used to playing the 6th string by shifting some melody exercises up 5 frets and down one string. It's not good to "avoid" the lowest melody string, better to really practice using it instead.