Here is the file. There are other ways to do this, but I used a union query of three queries. For some reason I could not get it to sort correctly. I needed one more query just to sort. The final solution is qrySortedMinMaxLast.
So if you went with the EVA design, you could do a version of this to have one query that returns Min, Max, Last for every reading. If you keep your design you will have to do a lot of individual queries. That could be over a hundred. However, there are other ways if you keep your current design. May just take some extra work. The real difference is do you want to do the work up front with the EVA or the work on the back. Again what you are doing is not incorrect, the EVA is just a different approach that can simplify things. It can be very efficient if you do not take all of those readings each investigation.
If you want to go with the EVA we can walk you through and help. I gave you a pretty good start on the table design. I will demo a form. Until you see it work it is hard to understand.
If you keep your current design you really only need one attachment field. No need for multiple attachment fields since you can put unlimited documents in one field.