I do not see how the lbs of the wing would effect a positive buoyant piece of dive gear. Yes you may need more weight to go down using a 7mm, but this is offsetted by the 7mm wetsuit. According to the shop I bought my ET from. the 24lb wing should have no issues with my steel 120 tank, 3mm wetsuit and a 30cf pony bottle. Now throwing on double or side mounts is not going to happen, but that is not what this BC is designed for.
It is one of the criteria deciding wing size. The reason is this. Your 7mm suit will have 20lb of left on surface. But at 100ft, it will be compressed, has minimal buoyancy, for simplicity of discussion, let's say it is 5lb at 100ft. You lose 15lb positive buoyancy just by descending to 100ft. Your wing needs to compensate for that. See how's suit buoyancy can affect wing size. Keep in mind, BC= buoyancy compensate. It needs to compensate for all things that can change buoyancy in your dive. Lead is not one of those things.
As for whether 24lb is enough, let me quote Tobin here. Your BC should fulfill this requirements:
1. Float you comfort with head above water with full tanks
2. Compensate all lost in buoyancy
3. Float your rig without you in it.
120 tank + 30 pony = 150cf of air/nitrox. This is 12lb. You will be negative by at the beginning of your dive. 24lb wing leaves you 12lb to fulfill #1, which should be OK.
Your 3mm suit doesn't have 12lb to lose. So you are ok too. But if you wear. 7mm, you won't have enough.
#3 can be easy archive if you have a balanced rig and weighted properly.