New Class Keys / Extending modResource object#

I'm not 100% sure that this is the right way to go, so I'm asking here

Before I was ware of MODx Ie built a large classified directory site from scratch, using my own (limited) framework.

My client is now asking for a CMS, and I thought of MODx.

What I've done so far is very extensive, so creating snippets and template chunks to convert it to MODx is going to be nearly impossible.

However, my framework can be limited to just supplying the raw data as a PHP array or output as XML or JSON, so what I was thinking of is to create more modx class php classes (eg moddocument, modweblink - ie extending modresource.class.php) that would interact directly with what I've already written.

Does this sound like a sensible approach......or not....?

I think creating snippets to do that would be much simpler; extending the Resource class could get pretty complex. The snippet would interact with your existing code in pretty much the same way, but you can just create the Resources and use the Snippet to handle returning the output from what you've created already.