I would like to do self-paced SP2013 training and eventually development at home using my own SP2013 sandbox (S-Server or Foundation), as I don't want to interfere with the production environment at work. What steps do I need to take to run either version in an Azure VM on a new iMac w/ 8GB? Do I need a business license to purchase and use either product? What about the OS? How many are needed for a training environment? Would SharePoint for O365 be incompatible for training using SP2013 training materials?
If you're responsible for SharePoint development in your organization, then your organization should definitely be providing you with a sandbox environment to play around with. If they're not doing that then ask around and try to get that done. You can't be expected to produce quality work if you don't have a place to safely make mistakes.
If you really need to roll your own, and have access to Azure, then a pre-built SP 2013 environment should be available for you to spin up. Make sure to deallocate when it's not in use, those things can get pricey.
Having an Office 365 environment would allow you to do a subset of what can be done in SP2013, so its value to you in the short term would depend on what specifically you're trying to accomplish.
But in the long term it provides you access to the next generation of technology, which can only help your marketability going forward. If you're looking to solidify career options in this field then Office 365 experience is going to be a must-have at some point.