idol talaga si iluvdetailing! hehe
Oist... di ako magaling, basic knowledge lang. Baka batukan ako ng mga tunay na gurus.

if the HU only has one pair of preouts (rear), can i connect that to one subwoofer (bridged)?
Yes.

If i'm using the rear preout as described above, can i still use the rear speakers by using the HU to power it? (so mangyayari, ginamit ko na yung rear preout, ginamit ko pa yung rear speakers from the HU). Is that ok?
Yes. Adjust mo na lang yung equa ng HU so that the rear speakers will only play lows if possible.