Woah buddy, hard decision. If the 12"s are solobarics, choose two 12's. But then with that L5, that has the surface area of an 18" subwoofer because it's a square. The solobaric and kicker amp would be a great combo.
Make that box huge, as big as you can. Like 5 cu ft. If you need any help with building a box, send a message. All the sound depends on the box. Well about 70% of the sound depends on the box.