Guys that have lowered 5" don't seem to have a lot of probs with alignments that I'm aware of. That's 3" coils, & 2" spindles. Spindles don't affect the alignment, so technically the 3" coils are the same as what they've done. Just make sure the upper control arms have had the adjustment knock-outs punched.
Shock extenders aren't so much for the ability to run a certain length shock. Shocks come in a lot of different lengths so there are more than a few choices there. What they do do, is correct the angle of the shock, as the lower you go, the more laid out they become, causing them to act more like levers as opposed to absorbers. The ride quality would certainly be compromised without them on a 5" drop. I'd use them.