Hi,
The different productivity levels are intentional for balancing. Stone and foundation go up to 30 because they're your main resources throughout the game - you'll need tons of them! Stone brick (5) and calcite (3) are kept lower because they're intermediate products. If they had high productivity too, it would stack with stone productivity and become way too powerful.
Other planets:
Right now the mod focuses mainly on Nauvis gameplay. The other planets (Vulcanus, Fulgora, Gleba, Aquilo) are mostly vanilla Space Age. There are a few planet-specific recipe tweaks (like sulfur on Vulcanus uses the original recipe instead of lava), but the core experience on other planets is unchanged. More planet content might come in future updates!
Foundation limit (5000):
Yes, that's by design to push you toward space exploration. Once you hit the limit, you'll need to look beyond Nauvis for more expansion options. Think of it as the island saying "time to leave the nest!" :)
Landfill research:
Good catch! You're right - landfill is craftable from the start but there's still a tech for it. The research exists because Gleba needs it as a prerequisite. I'll look into cleaning this up in a future update.
Thanks so much for playing and taking the time to give feedback - it really helps improve the mod! If you run into any other questions or issues, feel free to ask. Enjoy your lava island adventure!