Hi J and welcome to the forum,
The good thing about drop-ship advice is that it is mostly generic, so you can adapt it to suit most countries. In regards to a business licence, if you intend on operating as a business in SA, then you would certainly require such for your taxation requirements.
That could also possibly assist you where suppliers require a tax id, although a tax id is mostly required by wholesaler's not so much drop-shippers. Plus, even if a drop-supplier does request a tax id, they will usually wave that once they know you are an international customer.
So from a local taxation perspective, you may consider getting that.
Outside of that. the only restrictions you need to be aware of would be what can and what can't be legally imported into SA and any import tax implications your SA customers may face on your sales. Information such as this can easily be sourced through Customs.