Hi Neil
I really don’t see any restrictions here at all, depends what you want to achieve. Best to start by coding up a static html page outside of MODx using ElastiCSS - you could use your WYSIWYG editor for that if you wish. Then when you are happy with it you can drop the markup straight into a MODx template, simple as that.
I always create a ’header’ chunk for the <head> section, and a ’footer’ chunk for my site footer as this code is going to be the same across all pages and templates. You could create different templates for 2-col, 3-col or whatever layouts you want to use from ElastiCSS.
It’s then just a matter of replacing, say the content of the <h1></h1> tags with [[*pagetitle]], main copy with [[*content]], and anything else you might want to make editable via MODx.
Check out one of these
tutorials for a quick walkthrough and setup of a basic site - it will be 30minutes very well spent!