100W solar panel seems like overkill. I'm curious what the minimal size panel one would need for 24 hour usage. Assuming 5 hours of usable sun, it would seem like a 20 W panel would be sufficient.
you don't get a cookie for installing less panel. you just get headaches on low-sun days. and your battery won't last as long, as it has to discharge deeper and more often.
Since the solarpanel is more than half of the budget, I would think, you can actually buy a cookie for ordering a cheaper one.
I think it depends where you live and if the setup should also run in the winter.