How to extend product fields and filter them?

Hello again,

on my way building up an Etsy-like store, and after digging for hours, I have more questions I couldn't clarify:

1) How can I extend product fields?

2) How can I do filters on those fields?

I need specifically:

- Size (for shirts, dresses, hats, etc.)
- Shoe size
- Colour
- Material

Then I need to filter on those fields like they do here:

I have tried MP Product Search Widget but it doesn't seem to work for me.
Someone suggested I contact the author, and I'll probably do that next.

First I need to know what is the 'right' way to extend the product fields and IF using 'MP Product Search Widget' is recommended and would allow to extend filtering on those custom fields.

Looking forward for some light.

Thanks a lot!