What are some things I need to know as a 3D Art Hobbyist if I wanted to design my own Epic style Minis?

So long story short I've been doing 3D art as hobby for years and 40k is something that has come up from time to time, and in the last year I've started to really get into 3D printing, starting off with a Makerbot but quickly learning that it's limitations just weren't suitable for my needs. Eventually I found Shapeways and well, I think my shop really speaks for itself here! ;p

It all leads to the present where my 40k interest is growing and I've even incorporated 3D prints into my 40K Necrons a bit and with the potential return of Specialist games, of which I always found interesting but never had any hands on experience with before GW axed them, it's got me wondering how I might apply my skills to Epic and and BFG.

But knowing little to nothing about Epic in particular makes it a bit daunting to simply dive into so I bring it to you guys!

What are the kinds of things I would need to consider for possibly doing some Art for Epic?

I've seen it said that Epic is 6mm scale, but is it uniformly 6mm or is it kinda tweaked around with as needed?

Are there any rough standards for Model/unit composition or is mostly done on an army by army basis?

Or just anything else that you think would be good to know really, think of this as an exploratory mission so more knowledge is going to go a long way!

Thanks in advance for your time and responses!