Use the larger vessel... You'll want the extra space for when you degass/aerate it (until the 1/3 break)... Keep the 5 gallon for when you rack it the first time.
How strong are you looking to make it? Make sure you take an OG reading before you pitch the yeast in. Otherwise, you won't know if you hit your target OG or not. Since honey can vary in actual sugar content, the amount you need to use can also vary. If you want to get a better idea, then mix up an ounce of honey in a cup of water and take a reading (or double that if you need more for the SG reading). 1oz/cup will give you the OG equal of 1#/gallon. From there, you can calculate what you'll get with X#/N gallons... Just remember, 12# of honey occupies one gallon of liquid volume. But also remember to measure your honey by weight, not volume. The liquid equal is so that you subtract the correct amount of water from what you'll use/add to reach your target volume.
