Genuinely looks perfect. I didn't get a notification for this resource upload even though I'm following you, but luckily this mod showed up on the side. Thank god it did. It looks perfect. You added plenty of support for extra features like tanning and more-clothing use. Plus, it's drawn in the vanilla style. This should've been what Konashian drew all those years ago when he created this game. I haven't used it yet but I know that this review won't change. This is going to be a mod I'll be adding to all my characters from now on
Regarding the issue with the arm placement:
The cupping/holding breasts positions are a feature of animtools.
I'm not sure how this is implemented. Possibly the hands are placed relative to the breast mod's origin point so that the hand matches the position of the vanilla breast artwork? This of course won't fit the modified natural breast's shapes.
I don't think that I can do to fix this in the scope of the natural breasts mod alone.
Having an (invisible) symbol which designates the hand placement point, which is then used by animtools might be a strategy for adding compatibility for the hand positions.