Hi,
1. Thank for your feedback on the error messages.
We've added a patch for them. You can download the install package via the menu My account>My subscriptions on our website and install it on yours to get the patch.
2. When you have several wishlists, you always have a "current wishlist". And when you click on the "add to wishlist" button, it automatically goes into that current wishlist.
If you have a "HikaShop control panel" menu item to access the control panel on the frontend, you can click on the "wishlists" button there to access your listing of wishlists. On that listing, you have a column "current" and if you click on the star in that column for a wishlist it will become the new current one.