That is a combo that I have used with more than adequate success. It is a good, though not perfect, set up for all the reasons you have mentioned. You might want to search this forum for advice on how to use it correctly. Above all, practice with it some at home and make sure you know how to set it up correctly to stay warm enough before you get on the trail.
Most people seem to refuse to use the space blanket, but I highly recommend it. So does Tom Hennessy.
If you think you might be consistently below 30*, you might want to add the HH kidney/torso pads. You can compress( gently, they are fragile) all of these padsmain/kidney/torso) down pretty good, but it will take a little time and care. Also, look into a Garlington insulator to really beef up the SS, for negligible cost or weight. Place it down between the pad and the undercover.
With or without added clothes on top of the pad or beneath the pad in the undercover, check you adjustments and avoid any air gap at all costs. Any air gap will make the insulation about zero. Make sure that once you are in the hammock, the pad/space blanket ( and/or added insulation like a down vest) is in solid contact with your back. Make sure the space blanket is on top of ALL insulation, in contact with your hammock. If you add anything to the undercover, make sure the weight of it doesn't pull it down, causing a gap.
Did I mention to avoid any air gaps?
You might consider carrying a minimal 3/4 length pad mainly for ground backup, or even to add inside the hammock in case of record cold.
Good luck, and keep us posted on how it works for you!