I would suggest you start programming directly within Excel's VBA IDE.
This will give you more speedy results, allow you to use the macro
recorder to learn how its objects, methods, properties, and collections
work, AND you can test code on the fly more easily/readily during
development.
As far as your assertion that VSTO is M$'s replacement for VBA goes,
that's never going to happen! VBA has been upgraded for x64 and so I
expect they plan to continue with it as the default macro language for
M$O apps.
If you want some good reference material for serious application
development in the Excel platform then check these out:
http://www.appspro.com/Books/Books.htm
In any case, you'll have to learn Excel's object model if you expect to
achieve any competent level of automation skill as your employer
expects. Once you're familiar with developing directly in VBA then
maybe you'll want to resort to automating via some other language.
DLLs are a good idea (in any language). VBA projects support their use
via References to registered COM objects/libraries.
A word of advice regarding x64 versions and x32 versions; you need to
develop x64 VBA in Excel x64 edition, and x32 VBA in Excel x32 edition.
In the latter case, always develop in the earliest version you expect
your users will use your project with.
HTH
--
Garry
Free usenet access at
http://www.eternal-september.org
ClassicVB Users Regroup! comp.lang.basic.visual.misc