Those sections are called signatures, and yes, you’ll need to ask the printer how large the signatures will be. Books, magazines, catalogs, etc., aren’t printed one page at a time. Instead, multiple pages are printed on one large sheet of paper. The individual pages are “imposed” by the printer (which means the printer arranges them) in a way that when the sheet of paper is folded and trimmed, all the pages are in the right order within the signature.
Signature sizes vary depending on the size of the book and the size of the printing press. A typical signature might be 24 pages, so your approximately 100-page book would actually be 96 pages. That said, the printer can insert an extra four pages, but those four extra pages will, in effect, constitute a separate signature and will cost more since it might require a separate press run. Keep in mind that you need to think in terms of multiples of four pages.
You mentioned the pages being glued together. This would be called perfect binding, but are you sure it will be perfect bound? A 100-page book might be stapled or saddle-stitched instead, which is a bit cheaper. If the book will be perfect bound, you’ll need to allow for extra space in the inside gutter since perfect bound books can’t be fully opened without cracking the spine. There’s also the matter of whether or not the catalog will be self-covered or a separate heavier paper stock will be used for the cover.
Or as HotButton suggested, if the size and page count of the catalog hasn’t changed since it was last printed, use it as a guide. Also keep in mind that I live in the USA. The processes will be the same wherever you live, but the terminology might differ.
Just a follow-up on your sentence since it could be interpreted several different ways.
If you’re saying you think the signatures should be created as separate InDesign files, no, that’s incorrect. You only need to make one InDesign file containing all the pages for the entire catalog. The printer will break it down into signatures and determine the imposition depending on their needs.
Just be aware that the total page count must be in multiples of four and, if possible, those pages should add up to the total pages available in the signatures. Only using 28 pages in a 32-page signature, for example wastes four pages that you otherwise could have used. Likewise, adding 4 or 8 extra pages beyond what’s available in a signature will increase costs.