Nasty way or right way, i will leave that judgement to you :-)
Here is how I see it.... It does not matter what approach you take, you will have to do following at minimum:
1. Create new datatable(s)
2. Modify or create admin interface to assign your custom fields to each post unless you want to use some mechanism that will automatically assign custom fields to each post via extension.
3. Modify PostView in skin to display your custom fields.
4. Create extesion (to do any post processing on post etc.)
As you can see whatever approach you take, you have few changes to make any ways. The update for adcategories is very close to what you are trying to do. Part that may sound more complicate din that update is how it wants to pull advertisements. In your
case, you do not have to do any such thing unless you want to add some intelligence to extracting custom fields from post content itself.
So either way, you have some work to do.