One key detail you are missing when dealing with panel loops…
Do not panel loop your mesh more than once.
Create all your polygroups first then panel loop once. Undo as many times as necessary to get the panel look and feel you are after.
Double option in panel loops will create a inside mesh layer under the topology you see in the zBrush canvas. If you do not want that turn it off. However it can be beneficial.
After you panel looped you can use Deformation and use polish by features. If you use the solid dot your mesh will retain its volume. In other the words your mesh will not shrink to some small degree when using the polish by features slider. If click on the dot to make hollow dot, it reduce some volume on your mesh.
If you not certain about how many polygroups you need at given time, then you may need to divide your mesh into sub tools so that you can deal with various parts of the model one at a time. For example lets say you know how the top of the sphere is supposed to look and feel, but you are uncertain about the lower portion of the sphere. You divide the sphere into two sub tools. Work on the top half first.
Regardless of how may subtools, it is important that you only panel loop once per subtool. You have to establish your polygroups first as opposed to … Ok create a polygroup here and panel loop… now create a polygroup there and panel loop and so on.
Hope this helps!