Newbie questions

[Bigfootpete]

Hi,
I'm relatively new to speaker building - ok I've only built one pair of TL speakers from a kit...That got me interested in making my own design.

I am thinking of building a floor standing two way ported design, with a baffles to direct the sound zig-zag style out of the port (front facing).

My first question is...

Do I need to consider how the actual design will affect diffraction or phase? If so how?

2) Does the internal volume of the cabinet need to be optimal for the mid-woofer driver?

and last but not least
3) Choosing drivers - I have the Hiquphon OW2 in mind - what specs do I need to consider when matching with a suitable mid-woofer? Apart from slightly overlapping frequency.

Thanks.
P