Longer trips to unfamiliar territory are great! I did one myself from BN up the coast to Cairns, across the gulf, south through the red centre and then east via Charleville... absolutely fantastic with nothing but a watch, a WAC and a window.
I would however recommend talking to your CFI about what you would be missing on the structured solo navs they have planned in the syllabus. Once you know what is there then you can plan supplementary exercises to do along the way such that the CFI may let you include the hours you're planning into a 150hr course rather than requiring you to do the 200 hr course.