Hi Gilbert
My April-May from Le Puy to Pamplona in 2010 was an unforgettable experience. I left very late March, and I'm told that the Aubrac can be just too brutal before that. I encountered far more cold than warm days, even in late May, but, since I don't handle the heat, that's okay. (Please don't ask why I live on the fringe of the sub-tropics!)
I would recommend taking a Miam Miam Dodo guide and phone, since the route is shared with French holidayers who do portions of the GR65 for weekends and hols. It's nearly always possible to ring ahead in France, and, once you know your rhythm, you can organise quite a few days in advance.
Of course, there are other guides and sources of info. I suppose the main thing to remember is that the Le Puy route is not as busy as the
Camino Frances, but is probably the second busiest route, due, as I said, to its being the most popular stretch of the GR65. The good news is that there is an abundance of pilgrim and other accommodation.
I think your plan for a Spring departure in April is a good one. Easter and Paris school hols will create some strain on the accommodation, but one works it out.
Have you checked out the KiwiNomad's blog on her experience of the route? That helped and encouraged me before I left for Le Puy.
Best
Rob