100 things vertically in a gallery would be a lot to scroll thru. Can you break it up into smaller chunks? It would be better to have separate pages with a smaller amount (say 10) per page.
If you really want to use a gallery, it will work. You will need to add everything yourself. The gallery will "automatically" add 3, but you will have to do the others. I would copy and paste the 3, then grab all 6 and copy/paste those, then grab all 12, etc. Then you will need to change the fields manually, putting them in the order you want.
It may be less hand coding if you use a form. That would have the system do more of the work, as you can order fields by draging and dropping.
I would still look for a logical way to break things up. Your user would be very disappointed if they got 90 items into the list and something happened before they hit the save button and they needed to re-enter everything.
