General theory is to add 4 lbs for salt water. However, since you are putting on a little neoprene, you might want to start with 6 lbs. Then go up or down as required.
Do a bouyancy/weighting check before your first "real" dive; then you will get that all squared away. Don't forget to take into account that an AL 80 tank becomes about 4lbs positively bouyant when you get to less than 1000 psi. So factor that into your weighting as well.
Since these will be your first post-certification dives, you may find that you require a little more weight than you thought you would. This is quite common: newly certified divers tend to hold a lot of air in their lungs because of excitement, not relaxing enough, etc. So don't be disappointed if this is the case.
As you dive more you'll find that you can start subtracting weight because your comfort level & control will improve.
Hope this helps,
~SubMariner~