1. No
2. No in most cases where it's held in your personal capacity and you don't sell it. If you sell it, then yes.
3. Yes. Even though it was never converted to ZAR, you have realised a gain as soon as it was used in the transaction you mentioned. The onus however is on you to declare it. If not declared, it can be considered as tax evasion by SARS and not avoidance.
4. No. Addressed in 3 above.
SARS might never become aware of the transaction though.
Tax evasion is a criminal offence. Tax avoidance is simply structuring your tax affairs in the most tax efficient way. There is however something that SARS considers as a Tax Avoidance Scheme.
Tax is also not just applicable to cash transactions but also where any financial value is involved.
As an example, if I own a property and gift it to my son while I'm alive, I would be liable to pay donation tax on the value of the property donation except for the first R100k at 20%. I could however overcome this by selling the property to him at a market related price. I would charge interest on this amount annually and write off R100k every year as a donation to my son. Eventually his debt to me would be zero and no donations tax would have been paid. SARS might consider this a Tax Avoidance Scheme but it would be for them to prove the intent of the transaction.
A good Tax Accountant should be able to assist but they don't come cheap. Tax lawyers are even more costly.