It is not possible to simultaneously complete 1200 diplomacy and 6 goods buildings with 12 total 4x4 plots while using only 50 clan totems.
12 4x4 squares= 192 squares excluding impediments.
For 6 goods buildings, that is at minimum 54 squares, 72 squares, or 90 squares, depending on goods buildings used.
Embasy is 12 squares.
For 6 3x3 goods buildings, that requires 270 population, which is 5 huts. Mead Brewery requires 216 population, 4 huts. For Wool Farms, 3 huts.
Need 50 clan totems requiring 100 squares for 1200 diplomacy.
So for 6 3x3 goods buildings + 1200 diplomacy :
54 squares from goods
12 Embassy squares
45 Huts squares
100 Clan totems squares
Total= 211
Total squares for 12 4x4 pots is 192. Without willows, this requires 14 total 4x4 plots (10 additional expansions)
Total for 6 Mead Breweries = 220 squares. Requires 14 total plots (10 expansions).
Total for 6 Wool Farms = 229. Requires 15 total plots (11 expansions).
Alternatively with Old Willows:
54 squares from goods
12 Embassy
45 Huts
72 Willows (12 Willows, or less with combination of other diplomacy buildings, or bare minimum 68 squares with 11 Willows and 2 Runestones)
Total= 183, 179 bare minimum theoretically. So it is theoretically possible with Willows provided impediments do not hinder this production.
Conclusion: It is very unlikely that simultaneous 6 goods buildings and 1200 diplomacy would be achievable in 12 4x4 plots even using willows. However, using willows requires 8 hours of dead time with no production. That is 7 additional hours compared to the hour required to build clan totems.
Per new requirements of 4 goods buildings + 1200 diplomacy:
36 from goods
12 Embassy
36 Huts
100 from Clan Totems or 72 from Willows
Total= 184 with Totems excluding complications from impediments and all roads. Theoretically possible with Totems but unlikely with 12 4x4 plots (Again 192 spaces). But that might actually be physically impossible if I took the time to look at how that would work out on the actual grid. 156 spaces with Willows.
I am not sure previous posters were referring to 12 total 4x4 plots, but am inclined to believe they were referring to 12 additional expansions for a total of 16 plots. Regardless, given the ability to build diplomacy to satisfy the quest requirement, then tear down quickly and build 6 goods buildings, means a difference of at least 7 hours once the change is made to require simultaneous completion. This would likely be a higher real increase due to the additional space requirements for additional expansions.