When I have all the lowlands explored with level four guilds and a level three cursed foundry should I upgrade my guilds to SOS or keep building guilds
The fastest way to build as a hansel is to keep building guilds to at least the 20th highland. Once you've done that save up your gold and convert all highlands to lvl 1 volaries in one go. Save up another few hundred bil and convert all low lands to lvl 3 SoS. It sonds like a lot of money but as a guild hansel you'll earn it quickly, this method is far more efficient than building SoS 1 by 1. There are plenty of guides in the strategy section if you want more info.
Don't transfer to SOS, complete waste of gold . Keep with guilds and save gold for l1 vol upgrades once you've unlocked min of 10 hl