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Besides scrolls, we also need to discuss obtaining spells through learning.
I don't know what's best, but maybe we should play without level 3-5 scrolls at all?
Added 15 minutes later
As for the scrolls: either 2 Guilds up to level 3, or 1 up to level 5, as they wish. Otherwise, the Barbarians with the Citadel are completely useless. They aren't very good here anyway. Let's say they captured a dungeon, but they've already started building their Guilds up to level 2, so let them build 2 more Guilds up to level 3 tomorrow and use whatever they want, or build up to level 5 in the dungeon. It's up to them.
if a Castle has a level 3 or 4 Guild, and a level 3 Guild is built (in any of them), and they capture a Castle (or village) with a level 5 Guild, it's enough to have 1 level 3 Guild and 1 level 4 Guild. At least there will be a choice. And it's not about the resources for building, but about the fact that building in a newly captured Castle with a level 5 Guild takes 5 game days.
Added 6 minutes later
It's one thing when you start with a level 3 magic Castle and capture a level 5 one, and another thing when you start with a level 5 Castle and both players only get level 3 magic villages. You can see that building the Guild mainly affects the pace of building the entire Castle. Unless you plan to play until the 3rd week... (like resting after the first encounter until day 127 :D)
"Бороться, бороться, пока не покинет надежда, что может быть в жизни прекрасней подобной игры." В.Каверин "Два капитана".