The main reason currents SW mods don't use death stars are:
1. Really big things don't work too well when warping into systems. Often get crashes when warping into asteroid systems and ending up stuck inside the asteroid. The common solution has been to reduce the scale of everything/expand size of gravity wells so that in comparison, ships like the executor look large.
2. You can't actually blow up planets, its hard coded into the game. The most you could do it give it a really powerful bombardment beam to clear out planets fast, but that doesn't fit in with the lore.
3. Lucasarts isn't very modder friendly, so you can't get permission to use assets from their games. If it's for personal use, doubt anyone will know, but to distribute a mod using said assets may run into legal issues.
As for actual importing of models, the sticky on the top of the page is still pretty valid. Some of the mod team members may have some more up to date suggestions though.