You'll be able to do it in a day easy !!!
Just change the struts with the springs intact - no need to compress the springs at all !! Just pay attention when removing the rears to get the washers and bushes in the right order when you put them back. Also, you'll need a deep angled spanner or strut tool to remove the fronts - but if you've done it before you'll know all about it.
Adjustables are no different to normal stuff really - is your's damper or ride height adjustable (i'd assume damper or you'd be talking about coil overs, not adjustables).
If you're lowering the car it's always best to at least get the tracking checked - camber would be good too, but often rather expensive for a pucker laser geometry check.