I walked it last year in May so can't comment on the impact of Semana Santa.
Though Semana Santa on the VdlP prior to it did lead to a shortage of beds a couple of times and places also closed. I would say on the Invierno, on balance. you should be OK.
But if it were me, I'd be booking a day or two ahead just to be sure, as in some places there may only be one option to stay. (depending on your stages)
It's a wonderful route, and quie hilly.
But if you have a few days walking already as a warm up you should be fine.
I hit it after 40 days on the VdlP so hardly noticed the hills!
Well, they were not as bad as they might have felt......
Sounds like you are used to quite long days.
Allowing 4 days from Leon to Ponferrada, you'd need to do the Invierno in 11 days.
Average 24 km days.
It sounds easy, but the hills make it harder, and the stages often don't work out as you'd like.
But very 'doable' I'm sure.
I stuck to an average <20 km days on the Inveirno.
These were my stages. I go slow......... (green = short day <15 kms)
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