104, One sheet have two pages. front cover is two pages and back cover is two pages. In the magazines world (with ads on them) covers are usually counted as 4 pages. So when you say "on the third page of cover" you mean second to last page.
Those pages are usually not counted toward TOC so you start counting from the 3 page.
If you want your introduction pages to be on a spread you need to start them on the left side. So either on the second page of cover OR second page of actual magazine leaving you two empty spaces.
Calculation from printer should look like this for 68 page magazine:
Inside, 64 pgs.
Paper :Matt DC White, 130 g/m2
print : front CMYK, back CMYK (it's 4+4)
Cover, 4 pgs., 29,7 x 42,0 cm open
Paper: Matt DC white, 250 g/m2
Prepress : Impo
Print :front CMYK + 1 color, back CMYK + 1 color (all 4 pages have also spot color, if only first and fourth page had some other print it would be front CMYK + 1 color, back CMYK)