without seeing what you have there other then a description it is hard to answer your question about possible erosion. You should have base for your walkway and the base relates to your flagging material. Rememeber over time that any flagging you lay on soil will shift and move to some extent do...
new guy here. I have been picking away at my house for 18 yrs and came across this site. Great to be here and get input from other people when I need it.