Auto-translated
I suggest setting the hero level and excluding the Diamond map template.
Veteran is too easy, and Diamond is an unpredictable template; it can generate castles that are two days' travel apart. Also, there's a high risk of losing a castle due to a random attack from an opponent's portal.
And also, allow the Gnome to build a Tower – they are rarely chosen anyway, and this would at least make taking their castle more challenging. The Tower isn't too scary, but the Gnome is slower.