1. The Microsoft Store version won't replace the free version because it's not installed at the same place, but imported stuff will be available in both versions. I would just suggest to uninstall the free version.

2. Until now, updates are free.

3. The paid version offers the same features, 3D models and textures as in the GNU GPL version + all the models available at the free models page + the two textures libraries described at textures import page + auto update.