To make the whole mountain a perfect hearth vault you would roughly need 2500 banners or statues. Just did some interesting numbers.
Estimate wall size: 620 x 2 + 600 x 2 = 2440
2500 banners needs an upkeep of 1.8M authority per real life day.
17 days from full authority to 50k
32.8M max athority
2500 statues needs 2.6M athority / RL day
19 days from full authority to 50k
50.3M max athority
Even though statues look fancy its more wise to make banners.
Upkeep needs are staggering. You would need to pump 50k non boosted LP per day on a 400 int 400 charisma char to keep up with the banners. Let me just add that 2 edelvise Q10 would only give 8k base LP per day and that's on a 400 cha int character or 300/300 before full civil boost, on a 200/200 int char you would need 100k base LP. Some gear helps but I don't see myself ever bothering with making something like this. No one have ever made this big of a authority boost and I don't see the appeal to keep up with the authority drain. Its enough to slack of for 2 weeks and every blood hungry raging party will be knocking down your banners and tearing apart everything inside. I rather keep it simple and have people ram into the wall to find nothing in there.