i tend to always take an axe, just because i like to, it comes in handy when carving and cutting bigger logs as my folding saw is just a standard size...
in answer to your question though NO, an axe will never replace a knife, i have tried on a 5 items weekend, you can manage yes, but the finer work becomes very difficult and time consuming, the saw is always quicker than an axe due to the straight cut that is made through the log.
your knife should be fine as long as the handle is tight before you start battening with it, after all a mora stands up to it very well....
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
but i would say reduce the size of your blade to 3-4 inches, its all that is required really, that and a folding saw does the job, but then i nearly always have my axe when im away, be it for the day or a long weekend.....
try the smaller knife and saw combo first, it will cost less, £20 should get you both, just get a mora and a garden center folding saw, jobs a fish....
regards.
chris.