I wanna change my stereo to this one:
http://www.amazon.com/gp/product/B00...ef=oss_product

with this Microphone addon:
http://www.amazon.com/gp/product/B00...ef=oss_product

and with this subwoofer:
http://www.amazon.com/gp/product/B00...ef=oss_product

What do you guys think? Where should I put the sub to maximize space? And will I need anything else to make these all work in my Mini?

I'm new to the Mini scene btw. Just got my 2004 Mini Cooper S yesterday and I love it!

 

While your in there you might as well just buy a five channel amp and power all your speakers and get rid of the powered sub idea. They are junk and just create problems in the long run. Just look at a wedge/hatch box for a single sub. I have one and I can remove it whenever I want and I made a false bottom cover for my two amps that power the one sub and all the speakers.

Whatever you decide to do avoid low line converters. They will just give you feedback and distortion and result in a crap sounding complete system regardless of the HU.

If you want a powered sub I have a clarion 8in powered sub PM me if you want to know more, personally I'm an audiophile and like to have clarity over quantity.