a) The ISIN / WKN should be the same everywhere. If necessary, use different portals or ask support - that's what they are there for :-)

b) World ETF you can look for something like Prime Global, FTSE Developed and MSCI.

c) I would leave the old ETFs (if there are higher profits) and save in the new ones. After all, the TER of 0.19% to 0.15 or 0.12 is not much different. That's a few € a year.
1
image de profil
@MoneyISnotREAL With 50k in ETFs (which I'll soon be increasing to 100k), it's already a bit more than a few euros. 😉 I used to have more of your relaxed approach. But now that I'm dealing with shares and the like almost every day, I'm optimizing what I can.
@sobrius Optimization is definitely always possible. Maybe I got it wrong.

If you have larger gains on it, selling it (+taxes) will "cost" you more than just not continuing to save in the ETF and setting up a new one.

Since it's a percentage, it makes no difference whether you have €1 million in one ETF or €100k in 10 ETFs - provided the TER of the individual ETF to the weighted average of the others is the same 👌

Have you thought about how you are going to proceed?
image de profil
@MoneyISnotREAL I haven't actually entered an allowance for 2024 yet, but I just did. (Good tip from @DonkeyInvestor.) Because I've had losses in day trading recently, I can use it to switch the ETF with the largest share that is in the black tax-free. I will do that. As far as I can find a cheaper replacement in terms of TER, I'll just keep the others running.