Upgrading from 3.7 to 4.0

Your advice please!

I work for an end user in China and my knowledge about how Navision
and Microsoft and Solution Centres all do business is lacking, especially
in terms of licencing, regionalisation, localisation, exclusivity, etc.
We would like upgrade from Navision 3.7 to 4.0 so we can make use
of the new functionality offered by 4.0, which would be particularly
useful to us.
I have been working with Navision for 2-3 years and have quite a lot
of technical & application experience now. However, I have still have
still not been involved in doing an upgrade, so I was wondering if it
would be advisiable or not to attempt to do it myself.
Our present Navision 3.7 has been modified a fair amount, but nothing
like as much as others I have seen.
I realise that the new upgrade toolkit would assist a great deal, but I have
also heard that there are other important considerations which need all
to be addressed if the final result is to be just right.
The alternative is to find a company with much more experience that
can offer a quote to do the job for us.
This raises another question/issue.
We are not fully satisfied with the MSC we used to purchase the initial
product, licences and to make the initial modifications, but there is
no real choice here in China. Would it be reasonable/feasible to have
a Euro/US company do the upgrade for us and then get the required
Nav 4.0 licences, local Chinese objects and so on from the local MSC?
Could all licences, local objects etc. be acquired from elsewhere?

Many thanks in advance for your advice.....