Good to hear that worked well for your Grandfather. Every scale has its plusses and minuses, and everyone should do what suits them best. Personally, I feel that a good goal for anyone in retirement is to build a manageable and enjoyable layout, no matter what scale you choose. I have seen pictures of some excellent Z scale work posted here (including your own) so there is no denying what can be done in Z, and, of course, N scale has many, many followers here. It all comes down to what you choose. The layout I want will fit in a space of 8-1/2' x 9' in HO. It will involve a satisfactory operating scheme (suits me anyway), number of structures and scenic possibilities. It will not include a duck under. There will be a manageable amount of trackwork to maintain and it shouldn't take too many years to bring the whole thing to a reasonable state of completion. The layout should also be small enough to manage the multiple eras I want to operate the layout in without too many headaches involved in changing time periods. That brings me to the large selection of HO vehicles available, which is another thing I appreciate about HO scale and which will provide a "date stamp" for different era operating sessions. I guess the whole point of this ramble is that everyone should do what interests them, and select a scale that lends itself to those interests.
Excellent advice! My addition would be to ensure you have good lighting for your work surface. My wife swears by OttLite, and I use an LED headlamp to augment that as well. Good luck with your endeavours!