The Doctor's and Romana's incarnations may be simple to number, but the same cannot be said for the Master. The character is rarely, if ever, referenced to by their number, both in and out of universe. The number itself is quite complicated to come by, and is inconsistent when considering multiple sources. New incarnations are also inserted every so often, mostly between Beevers and Jacobi. This means the numbers would need to be changed regularly, which creates confusion for readers, both familiar and unfamiliar with any sort of numbering system.
One example of inconsistency is the numbering for Delgado and Pratt/Beevers. The television series never referenced Delgado's number. It did however call Pratt (and therefore Beevers) the Master's final (i.e. 13th) incarnation. The novel 'Legacy of the Daleks' later implied that Delgado and Pratt/Beevers are the same (13th) incarnation. However, the comic 'Doorway to Hell' flat out shows that the Delgado Master is not the same incarnation (making him the 12th at the latest) by having him regenerate. The audio 'The Two Masters' also makes use of a pre-disfigured Beevers Master, who is shown to be burnt to a crisp by one of his future incarnations.
Taking all of that into account, I believe placing numbers on incarnations (minus maybe Hughes and Pratt/Beevers) isn't very useful in the context of a Wikia page. Perhaps referring to each incarnation (or body) by their actor/portrayal or an in-universe alias/nick-name would be a more reasonable alternative.
Just for reference, here are the incarnations of the Master as reffered to by their portayal and some aliases.
William Hughes - The First Master
James Dreyfus - The Inventor (Big Finish First Doctor Adventures audios)
Roger Delgado - ?
Geoffrey Beevers - The Thirteenth Master
Peter Pratt & Geoffrey Beevers - The Burnt Master
Anthony Ainley - Tremas
New Adventures - Major Kreer (Virgin New Adventures novels)
Geoffrey Beevers II - Mr. Seta/John Smith (Big Finish Main Range audios)
Gordon Tipple - ?
Eric Roberts - Bruce
Doctor Who Magazine - The Preacher (DWM Eighth Doctor comics)
Short Trips/Companion Chronicles - George/Richard/Sailor/Maestro/Maestro Jr (BF short story and audio)
Geoffrey Beevers III - Don Maestro (Big Finish's Mastermind audio)
Alex MacQueen - Harcourt De'ath/The Doctor (Big Finish Dark Eyes/UNIT/Main Range audios)
Derek Jacobi - The War Master/Yana (Big Finish War Master audios)
+ Titan - The Boy (Titan Eleventh Doctor comics)
John Simm - Harold Saxon
Michelle Gomez - Missy
Doctor Who Magazine - Magnus
Edward Brayshaw - The War Chief
New Adventures - Felix Kriegslieter
Eighth Doctor Adventures/Faction Paradox/Philip Madoc - The Man with the Rosette/The Magistrate/The War King
who have all been implied to be the Master, but haven't explicitly been stated so.
"The debate was concluded by the short story Girl Power!, which shows eighteen deaths on Missy's Spacebook page. This results in nineteen true incarnations, not including possessed bodies. While the identities of the Master's incarnations pre-Beevers are not named by this story, it does account for every incarnation of the Master post-Beevers that have appeared in spin-off media." Tardis Wiki
What should be added?
After Survival there are 2 paths for the Master, one is that he stays as Anthony Ainley and eventually becomes decayed again, played by Geoffrey Beevers, and one where he gains a new body from the Tzun as seen in the Virgin New Adventures.
On a related note I think the Glorious Dead arc from the Eighth Doctor DWM Comics should be added, as they can easily fit in with Mastermind.