I've travelled all over Asia, and had no major problems (wandering hands on the HKG MTR). Most of it is very safe - I've been to all the places you list except Vietnam, and would happily return to any of them.
I never found Japan that easy to navigate, mainly because the best food is not that accessible (HKG used to be like this but has got better). Since it's your first trip, China may be a bit of a reach, but it's also very safe and fascinating.
Your travel may be bitter sweet - I enjoy solo travel, not having to compromise and do what I want when I want, but since you have recently lost your husband, I suspect there will be times when you'll miss being able to share what you see and experience with him. But - enjoy it nevertheless. I love Asia, it's fascinating and different and vibrant.
Have a great trip!