how to create a taxonomy term creation module (maybe with CCK??) for the node/add/* forms?

I need functionality to create hierarchical taxonomy terms from the node/add forms, because the site I am working on is to be maintained by a handful of very non-tech-savvy staff, and I'm sure the concept of creating terms before adding nodes will be lost - and categorizing after posting nodes will lead to broken pathauto paths, and this isn't desirable. I have tried CCK modules like Super Select Ultra (cck_taxonomy_ssu) but it has its limitations; what I really want is a simple text input field where a "directory path" can be inputted.

I have some PHP knowledge, and will attempt to create a module to suit my needs, but I don't really know how to start. What resources are there regarding Drupal module development? I basically want to explode the tag provided on the node page by the '/' delimiter where "term1/term2/term3" represents:

The site is required to have hierarchical URLs and navigation - I have installed modules including Pathauto, taxonomy_list, taxonomy_context to achieve this, and everything except content creation is working fine. At the minute I have got around the problem by installing taxonomy_limit, enabling free tagging and limiting the number of terms to 1. This works fine for flat-tagging, but the required 'directory structure' isn't flat.

The only issue I could find about this was http://drupal.org/node/19697 which is the original folksonomy module for D4.6/D4.7 and although a few people seemed keen to implement hierarchical free tagging, it was apparently never followed up. The main arguments against it there were users populating the taxonomy with hundreds of synonyms and typos, but since the site I am building will only be contributed to by staff, and as I am also hoping to use the auto-suggest that I already get on the free-tagging form, I don't see this being a big problem.

Thanks, Jonathan