Hi Farai and welcome to the forums

No one-stop shop for all aspects exists at an acceptable price - although in my experience a couple of companies can provide you with the overreaching essentials in most areas to help you move forward.

The two major suppliers are Employment Conditions Abroad (ECA) and Mercer. They provide high-level services and  give excellent guidance - however they will also insist that you  make use of additional, specialist, local country-specific advisors in the areas of  employment law, immigration and taxation/social security. This will require your company to acquire some basic skills in managing international assignments since there are few "off the peg solutions" that work for everyone.

If you really want a "one-stop shop", you must be be prepared to spend a ridiculous amount of money with one of the big international legal firms. they will be more than happy to

• provide advice from each of their top local specialists in each country 
• appoint an international coordinator across all the countries concerned (ensuring that everythingg yo uintend to do complies with both both home and various host countries legislation - employment, tax, social security, company law, immigration......) 
• charge you for this very intensive service of coordination

In reply to Ray:

Therefore, Farai, your employer may as well take on ultimate responsibility and control of the process but still with the benefit of fully-comprehensive advice and guidance from these experts - it's not all that much more hassle to do it that way and at least someone in-house will be more likely fully to understand and effectively respond to unexpected / unanticipated things of which there are usually some!

In reply to Ray:

Thank you for your response Ray. Much appreciated!

In reply to David:

Thanks for that David!