Ginger is very exhaustive crop which require more nutrients. The dose of fertilizers application depends on soil type, region and cultivation practice. So it is always better to go for soil testing before planting.
Please provide more information on variety you are growing , soil type, exact location etc.
1. According to Indian Institute of Spice Research, nitrogen and potassium should be applied at 2 to 3 split dose as a top dress at 45, 90 and 120 days after planting. But phosphorus should be applied in full dose at the time of planting at the base. Please see the attached screen shot for more information.
2. It is very hard to tell the ideal height since it depends on cultivar which you grow, climatic condition and management practices.
3. GA3 is generally used for fruit, vegetable and leaf crops. Normally not recommended at this stage of crop.
4. For higher yield you can apply micronutrients as foliar spray (@ 5 g per liter) during 60 and 90 days after planting.
5. Farm yard manure or compost should be applied only during initial soil preparation and at planting time since they take more time to decompose and release nutrients to soil.
Soil test based fertilizer recommendation
Improved varieties of ginger