Dear All
Based on the replies, I read:

- Using a single key pair (old) even for multiple transactions isn't an issue, with the exception of privacy concerns.
- Ensure that the Electrum clients are up to date
- Ensure that the fee is "appropriate"
- I mixed up some concepts: No need to download the whole chain (just recalled that the client shows the current fund level on the key which is from where I got this)

I would say this clarifies my concerns.

My primary concern was that there is no way I can "lose the coins" this way (naturally excluding compromised machines and incorrect target addresses).
Like e.g. it not being able to return the remaining funds (these concerns were answered or something similar.

I'm a bit paranoid because back in the days I was unaware that there could be multiple key pairs in a wallet, had a backup of only one of the keys in the wallet and was wondering why the balance was off when I imported it to another instance... Fortunately I did learn the reason and found the other key, but this kinda left me scarred in regards to making mistakes in the future.

Regarding privacy, "this isn't an issue" as the current and all future transactions will go to a single trusted destination.  I know it's bad practice, but as long as it doesn't result in missing coins, it's acceptable.

I would like to express a very big  *THANK YOU* for the helpful replies I've gotten!! This was highly appreciated! In case there are any points I've missed, I'm still more than grateful for having these pointed out!

Best regards
Richard

Hello Everyone
I have the private key of an old wallet with a bit of bitcoins (dating back before segwit ~ 2013). The key is completely offline.

What I've done is the following:
- Created an Electrum wallet with the key (old type single key, no seed)
- The public key showing for the wallet matches and I see the transactions for the old key (so far so good).

What I would like to do is:
- Install Electrum on another internet enabled computer, downloading the blockchain and creating a wallet (like above) using the. public key.
- This should allow me to create unsigned transactions (?) which I would then transfer over to the offline computer to be signed, transfer the signed transaction back and publish it.

My question is:
- Are there any issue using the "old style wallet"?
- If I only use parts of the funds, is there any issue with the the rest "remaining" on the old key (can the "return" amount be sent to the old key)?
- Are there any other risks with this legacy approach? (excluding either computer being compromised)

My concerns are (generic concerns without any data to back them up):
- That for whatever reason the transaction would not be accepted
- If a "chunk" is sent exceeding the amount of the transaction, the return amount wouldn't be correctly returned
- I couldn't use the same key pair again

I highly appreciate you feedback

Best regards
Richard