The 5 M's is a strange co-incidence. In all of history, based on a 1-5 query, it was only seen for the first time on 4 March 2023, the 3-0 home win vs. Raith Rovers:
David Mitchell, Jack McMillan, Harry Milne, Connor McAvoy, Aaron Muirhead
Most common surname letter in a starting eleven is 7 (M's again), seen only in 1988, 3 times in close proximity, firstly in the 1-1 midweek Scottish Cup draw at Station Park on 3 February 1988:
Archie MacLean, Alan Dinnie, John Workman, Bryan Purdie, Budgie McGhie, John McCormack, Pat Kelly, Willie McGuire, John McNaught, John Mitchell, Ian McDonald
Re the close proximity thing, will skip that on the grounds of time constraints, if you don't mind.
Most common surname in the first-team A-Z:
25 - Smith
24 - Robertson
22 - Wilson
19 - Brown
19 - Campbell
17 - Stewart
16 - Murray
14 - Ferguson
14 - Gray
13 - Gibson
13 - McDonald
13 - Thomson
Actually, we recently passed a club-record in that regard. 24 games in 3rd place is the longest run in the same position when considering mid-table positions only. The previous joint-record (20) was set in 6th place (1915) and 9th place (2015).