The strengths/challenges talk can happen as a simple acknowledgment of the child's experience. When he notices an issue, you can share recognition of it as a challenge.
I had forgotten that you only had an OT suggestion. I think you should pursue the neuropsych-- knowing is always better than not knowing IME.
ITA. Not having an official diagnosis doesn't have to be limiting when you talk to your ds - let him know that you and the teachers at school (or whoever) is working to help figure out why certain types of things are more difficult for him than for other children.
Like a few others have mentioned in their replies, our ds was *very* aware that he wasn't able to do things other students seemed to be able to do without thinking about it. He was aware of it long before we realized it as parents, and it impacted him in a much larger way than I really understood when he was first diagnosed. It wasn't until we'd actually talked to him about it and let him know what we'd learned about his diagnosis and how it impacted him that we realized he was so very aware.
It was also such a huge relief to him to have people actually help him. We parents often see accommodations, remediation, pull-outs, push-ins etc as making our children appear to be "different" - but my ds saw them through a very different filter - he already knew he was struggling, and having extra help from school staff, having accommodations etc made him feel like school staff *cared* and wanted to help him be successful. I used to look up stories about successful dysgraphic/dyspraxic adults to share with my ds when he was discouraged, and there seemed to be a common thread to so many of them - the never-failing support of either a parent or a mentor or a teacher who cared. It may feel really hard to talk to him about it, but years down the road what he's going to remember is that you *did* talk to him about it and that you advocated for him and supported him. You may not realize it now, but by sharing with him and advocating for him, you are giving him something so much larger and more important than the things that dyspraxia (or whatever it is) have taken away.
Best wishes,
polarbear