There is a simpler way actually. I just found:
import matplotlib.pyplot as plt
# We prepare the plot
fig, ax = plt.subplots()
# We change the fontsize of minor ticks label
ax.tick_params(axis="both", which="major", labelsize=10)
ax.tick_params(axis="both", which="minor", labelsize=8)
This only answers to the size of label
part of your question though.