Help with new HU and advice on speakers e36

I am driving a 1994 325is and it has 10 speakers in it and currently has the stock head unit.... I will be replacing the factory head unit with http://ift.tt/13XfgUa



Which comes with an adapter supposedly to fit my car with no problems http://ift.tt/13Xfevf



Currently at my disposal I have multiple subwoofers, but I plan on using 2 12" subs in the trunk using this amp http://ift.tt/1Amwsk4



I also have this amp that has a 10" sub on it, but will not be using it unless I can run both 12's and the 10 off of the soundstorm amp, or somehow bridge the amps if that's possible with these models... http://ift.tt/13Xfevn



I also have a capacitor to lessen the pull/drain on the battery



I am new to audio systems and was given these amps and the subs for free from a friend because they would not fit in his 350z, anyways my questions are as follows....



With using the new HU would I need to change the factory amp, or will it work through it?

Will my factory speakers need upgrading and how easily changed out are they? (20 years old prob wouldn't hurt getting new)

Will the Rockford amp be able to replace my factory one?

If not, can I somehow connect the two amps to get more power to the 2 12's?

Or even though its unnecessary run the 10 and both 12s at the same time with what I have?



Any wiring diagrams or pictures is always helpful and as always show off your own set up if you want!

Help with new HU and advice on speakers e36