Sometimes these small detail questions are hard to answer, but welcome and good luck.
I filled the holes in my fiberglass with pale yellow acrylic bathroom cault. It matched very well, but may not provide the structure you want to paint over it.
Yes, I believe the velcro was original. That's what I've found in my 75 Sovereign
and 77 Safari. I doubt you can buy the uniquely shaped curtain, but you could give the factory a call and see what kind of things they stock--seems like "expendables" like shower curtains would be in demand.
As for hanging you blinds, we'd all like to see your solution. Post photos!