Should I turn off my primary SIM?
No. Keep your primary SIM on so calls and texts still reach your normal number. Just turn off Data Roaming on that line so your home carrier cannot charge you for data. Then set the eSIMion line as your data line.
The setup that works
Your home SIM stays on with its data roaming off. It receives calls and texts as usual.
The eSIMion line handles all data, with its data roaming on.
That is the whole setup. Verification codes from your bank still arrive, and your maps and messages run on the travel plan.
One thing to know about answering calls
If you answer a call on your home SIM abroad, your home carrier's roaming rates apply to that call. Receiving texts is typically free, but check your carrier if you are unsure.