This would be a good place to start for all sorts of information about cyclocross … http://www.fluentincross.co.uk/
and here … http://crossjunkie.blogspot.co.uk/
Same guy, but the first website is the new location/format.
I’m not really qualified to hand out cx advice, so I’ll leave that for others. The only thing I’ll say is that like you when I was setting up my cx bike the main purpose was for doing the 3 Peaks, and I had the same bar width dilemma.
In the end I went for a 44cm Salsa Cowbell 2 bar as I wanted it fairly wide for off-road handling. This bar is too wide for my shoulder width really, but it gave me some confidence initially.