I've done the traverse from the top of kuffner ridge, over Maudit to Mont Blanc. It's all relatively simple, though there is a big cornice hanging over the brenva glacier that is worth staying well back from (speaking from personal experience). The route from the top of kuffner down to tacul looked steepish though we weren't going in that direction so I don't know for sure.
If you decide to go and down the standard route to the col du Midi, it's all pretty straightforward except for one steepish section, maybe 100m or so. I think this bit had fixed ropes for most of it (though don't quote me on that as I was tired at the time). The descent down to the col is through a pretty ugly icefall. Not technnically difficult but several guys got wiped out last year when a serac collapsed.
The lower Mer de Glace is cruisy. In high summer it should all be white ice. The moraine from the junction with the Lescheaux glacier is minimal compared with stuff in NZ. Still, if you want a quality detour instead of trudging down the glacier itself, there is a good high level hike that runs from the refuge de la couvercle through to nearly opposite the ladders at the mer de glace train terminus. The ladders to get up and back down again are crazy and worth doing.
Also, if you're not already a member of NZAC then think about joining up as you get reciprocal rights in the club alpin francais huts. If you're going to do the whole climbing in Europe thing then you might as well enjoy the bed, breakfast and dinner with wine at and not pay through the nose.