Self employed in Montenegro working with non-eu clients

There are many facets to tax, which could be a red flag on cash flow.

I provide services to non-EU clients USA specifically.  Id like to start a new business in Montenegro. Im not sure which route would be the best to take in terms of costs, or what the details would be yet. In many cases tax would be stated as only 9% but one forgets about the tax rate (20%), tax treaties, deductions, social security and stamp costs. Im likely missing more here which brings tax to a much higher level.

My plan:
I can either keep my South African business which pays my salary (I am self employed) as a Montenegrian temp or permanent resident

I can either start a Montenegrian business which pays my salary (I am self employed) as a Montenegrian temp or permanent resident who is a South African citizen

Notes:
A)In these cases I found that USA and Montenegro share no tax treaty. Montenegro also has no treaty with South Africa.
B)While Montenegro is not EU yet, it does require TAX on invoices
C)USA would then withhold 30% of the invoice.
D)Im sure there are other hidden costs i.e that one would need to pay. Social security, business insurance etc.

Questions:
- Does anyone here have experience with this ? or know more about taxes in Montenegro ?
- Do I need to add VAT to my Invoice to USA ?
- Which is better from a low tax perspective:
-- purchasing a property as a resident, and creating a business which employs me.
-- purchasing a property for the business, and i as employee work and live there.
- My wife and I are employed by the same business, does she need to apply too ? If she applies as my spouse, can she work and source income from foreign companies as employee ?