...what do you do about the legal aspect of allowing the version downloaded from the Internet to be used only within the intended scope
One does not allow a version to be downloaded from the Internet to be used only within the intended scope. Produce a product that can only be used within the intended scope because users will not oblige themselves to your software license if they can re-purpose your software for other means.
In general, a software license is just words and numbers, glossed over and skipped during installation or never read altogether. Though legally binding under the DMCA, it is better to ensure any functionality you desire to and desire not be designed upfront.
The only good a software license represents is to prevent your intellectual property from becoming mine. However, I can always run your software and produce a competing product off your ideas from what I see (not from code through de-compilation).
Thus, try to protect yourself as much as you can to the extent of your resources and the law.
Is there a standard procedure / contract for this - i.e. are there documents in the public domain for this or can I take one from another software vendor, tailor it, etc. Or, do I need to hand crank it - i.e. get an accountant/legal-person to write it up
Depends upon what you are trying to achieve. From your question within the bulleted section, you would need to tailor your software and your software licenses to support those but know it is not entirely possible to constrain user action in all circumstances. Microsoft can certainly attest to that but they have the means to legally prosecute infringements and that, I think, is where you should focus.
Certainly get legal counsel or advice from a trusted source and do whatever else you feel necessary.