If you use a Champagne yeast, you will definitely need to backsweeten as they will take your batch bone dry as Malkore points out.
You have several options depending on how you want to do things:
1) If you want to keep the ABV to around 12%, mix up the must to a gravity of about 1.090, which you should be able to do with something around 4.5 pounds of honey in 1.75 gallons total volume. Save the last 1/2 pound of honey to backsweeten it after fermentation has finished, and you have stabilized it to make sure they yeast won't ferment more.
2) If you want to keep the ABV around 12% but don't want to backsweeten, try making the must to a gravity of about 1.100, which will should take the full 5 pounds in about 1.75 gallons total volume. Then ferment using an ale yeast that will go to around 12% such as Nottingham.
3) If you don't mind the ABV getting to 14%, you can start with a gravity of of 1.115, which should be reached with the full 5 pounds in a total volume about 1.4 gallons. Then ferment with 71B (or another 14% ABV yeast). That will leave you with some residual sweetness when the yeast gets done.
The key to all of these is go by gravity and not by honey weight, as the variability in moisture content can add a good bit of error when going by weight. By using the hydrometer, you can get what you want. In each of these cases, the yeast should be rehydrated properly, and you should add nutrient/energizer and aeration.
I hope you get a great batch.
Medsen
