Rated by Nezo

The difference is significant:

Weld:

1. First tries to weld edges — it starts with edges where both sides are selected, and if none are found, it attempts to weld edges where only one side is selected. If there's nothing to weld, it performs a Stitch operation between islands (It turns out to be very convenient.).

2. Weld can also merge vertices based on distance.

Stitch:

1. Cannot merge vertices, it only performs stitching.

2. Has a Stitch Between option — select two islands, and Stitch will be applied at the shared edges.

But that’s not all — these operators are separated because they’ll continue to improve and become more distinct over time.

And by the way, you won’t have to wait long for updates: in the next release, Stitch will get a padding option, and both operators will gain support in the 3D viewport. You can already head over to the Discord links to find the latest Pro version of the addon and ask any questions you have.

You can not pack textures into a .3ds file, they are always linked. Put the textures into the same folder (or subfolder) as your .3ds file and they will be assigned to the model by import. Have a look into the manual to learn about the texture nodes setup.