The minimum records for a BIFF 8 file is not absolute, because it depends. If you use Excel to create an empty workbook, using Excel 2002 on Windows 2000 you'll get 146 records in the BIFF8.
The Global section is layed out as follows:
Then, there are three sets of the following (one for each worksheet)
The PHONETIC (00 EFh) record can be ignored, probably omitted, and Excel will continue to consider the BIFF8 record to be valid. Excel writes the PHONETIC record ID, the record-length count, and the following 6 bytes 00 00 37 00 00 00 for each of the 3 worksheets.
0x1c0 XL9FILE This record identifies a file as having been written by Excel2000. It's a zero byte record. This record should not need to be written
0x1c1 RECALCID This record contains an ID that marks when a worksheet was last recalculated. It's an optimization Excel uses to determine if it needs to recalculate the spreadsheet when it's opened.
0x105c ClrtClient This record contains RGB quads for the foreground, background, and possibly the neutral colors in use when the workbook was saved. This record shouldn't need to be written.
0xef PhoneticInfo This record is for internal use only, and shouldn't be written.
The EXTERNCOUNT record was used in BIFF7 and earlier, but isn't used in BIFF8. In BIFF7 and previous, EXTERNSHEET records form a table of external references. The EXTERNCOUNT record provided a count of those records. In BIFF8, the path and file name have been moved to the SUPBOOK record, and the EXTERNCOUNT record is no longer needed.