Total cost of buildings is 18.305T not 18.350T. In addition total lands cost is 47.760T and the grand total for osmon rai is 505.385T. I used the numbers in OP. Thanks for this. Helps me work out my build strat
Would it be best to build as many lvl. 1 spy buildings as I can, or build 1 and upgrade it as best as I can?
Personally, while land is a price you can easily afford i'd say buy as much as you can. Though the higher level buildings give great plunder increase so either or tbh.