Be sure to eat plenty of gluten between now and your gastroscopy.  Stopping gluten too soon can lead to false negative results.  Plus, in case you do have celiac disease, you might want to eat all of your favorite gluten-full foods while you can!

I could mean that: You have celiac disease but caught it early, before villi damage (especially true if you had a positive blood test for celiac disease--but there is the Marsh scale, and even minor damage could be caused by celiac disease); You have gluten sensitivity--approximately 10x more people have non-celiac gluten sensitivity than have celiac disease, but there isn’t yet a test for NCGS. If your symptoms go away on a gluten-free diet it would likely signal NCGS. You don't have either of the conditions and can eat gluten normally. From all of your posts I don't think you fit #3 here, so no matter the outcome a gluten-free diet might be your outcome for optimal health.

Yes, it would mean that the wheat starch contains less that 1% gluten. Gluten is not the only protein in the wheat kernel: https://engrain.us/understanding-wheat-protein-content/ It sounds like to me you have a good handle on the variables and hence the questions. The only way to nail this down any further would be to have the starch in question tested for gluten content. The FDA standard for "Gluten Free" is 20 ppm and the GFCO standard for "Certified Gluten Free" is 10 ppm. Even then, the question of safety could not be answered for all celiacs because of the huge range in sensitivity. For some, even 10 ppm is enough to generate a celiac reaction. So, I think it would be impossible to answer the question of safety of the wheat paste adhesive for 100% of celiacs but it might be possible to answer it for the majority, as does the FDA standard of 20 ppm.

Welcome to the forum.  If you can't avoid eating out due to work and travel, you may want to consider taking an AN-PEP based enzyme like GliadinX (a sponsor here), as there has been a lot of research that shows that it can break down small amounts of gluten in the stomach. I still eat out because I enjoy doing so, and I used to have issues ~30% of the time, but since taking these before any meal at a restaurant I haven't had any issues. I still want to support what @trents mentioned, which is the fact that it is still a much safer bet for celiacs to avoid eating out, as totally avoiding gluten is still the overall safest approach.

If you believe that the rash or other symptoms you have might be caused by gluten sensitivity, then perhaps you could ask your doctor to have you screened for celiac disease? Some of the symptoms you mentioned, with the exception of the rash and nausea, don't sound like typical celiac disease symptoms, however, the only way to know for sure would be to get screened.