Can I go to Nangang School after buying Guantian Farmer Apartment?

You can't. According to the enrollment brochure of Nangang School, the enrollment school districts of Nanchang Nangang School Education Group include Nanchang Iron and Steel Plant Dormitory, Provincial Forestry Transportation Group Dormitory, Provincial Measuring Tool Factory Dormitory, Fang Yue Village, Guantian Village, Zhushan Village, Changdong Avenue 1599 (a famous city with hundreds of millions of nests), etc., which does not include Guantian Farmers' Apartment.