No. The point of an eSIM is that the existing card can stay in the phone. What you do instead is divide the jobs clearly: set the data line to the destination profile and switch the home line's data roaming off, so the old number only receives messages and never touches the internet.

The most common cause is that the data line still points at your old number: a successful install does not change that setting for you. Open SIM management and switch the data default to the destination profile. The other frequent cause is roaming being switched off phone-wide, which stops a travel profile that works in a roaming state from connecting at all.

That depends on your operator and your plan, and it is a question for them directly. What you control from the phone is switching that line's data roaming off per line, so the old number uses no internet at all. How receiving calls or texts is charged is your operator's own condition, and not something we can answer on their behalf.

It depends on the model and the operating system version. Some phones store several profiles but can only have a limited number switched on at once; others support only one physical SIM alongside one eSIM. The most direct check is to open SIM management on your own handset and see how many lines it will let you have active together.

It depends how much you need calls or texts on that number. If you need one-time codes, leave it on but keep its data roaming off. If there are stretches where you genuinely do not need it, switching it off temporarily saves battery and reduces the chance of unintended charges — though while it is off, messages and calls to that number will not reach you.

If you rarely make calls and are worried about cost, set as default the line whose charges you understand best, and pick a line per call when you need to. Remember that this default only applies when you are the one dialling — incoming calls arrive on whichever number the other person rang, regardless of the default.