Hello Glen Loupias,
we are dividing modules on "pluggable" and "intrasite modules". The idea behind the pluggable modules is that you can take them and easily "plug" into another site. Usually when clients are asking us what kind of module should they develop our first question is on how many websites they plan to use this module.
You can find more about the module development and these differences in our developer manual in the modules overview section
Now, to your question. If the websites don't have to be aware of each other, I suggest you develop a pluggable module and deploy it simply through a single .dll file (take a look at the new approach introduced in Sitefinity 3.6
for this). Then on each update all you need to do is upload a .dll file to the bin folder of the websites.
If the websites have to be aware of each other, I would still go with this approach, but shared the data via the provider model pattern. More info on provider model pattern and Sitefinity can be found here
Any other approach in my opinion may cause more problems and complications than it would bring benefits.
I hope you'll find this information helpful. Let us know if there is anything else we can do for you.
the Telerik team