Product installation/server provision config question

Trying to figure out how to configure whmcs for the following scenario:

There are are a variety of products that require to be installed upon a host.
Customer can elect to have these products installed in one of three ways
1) on a vps that they bought previously from me (should be able to choose from a list of vps in their account as an option)
2) on a new vps that they want to buy from me
3) on a free tier, that is, on one of the servers that I make available where some amount of users will run on a shared vps.

I installed a test "Provisioning Module", and configured a Server Group and Server for a product, but I do not see how I can configure whmcs to have the options that I mentioned above. I would appreciate any threads or disc
ussion on how to best accomplish the above.

Thanks!