What would be the minimum required to successfully complete the first wing up to Saurfang to help people get their "Transmog" token? Would 10 people be enough or can we get away with less?
We did it easily with 8 players on 25man heroic including plague wing, blood wing and valithria. Some players had to leave at that point but I think sindragosa is doable as well.
If you just want the first 4 bosses you can probably get away with less.
Off-topic (kinda) but we did a 25 man guild run with 25 level 85 guildies for transmog gear. Was so much fun, ignoring all mechanics for the most part and zerging some bosses in sub 60 seconds.