I'm not sure if im understanding correctly, but i'd imagine a player on good terms with pirates should be able to land but no one else?
Pirates don't require you to be friendly to trade, so long as your transponder is off.
5 levels of pirate stations - nogunz, 1, 2, 3 combat sections, then mines, or those funny looking pike sections?
Nothing that high, it tops out at "3 sections" and then quality goes up for the 5th tier.
Will buildings have any differences based on the planet size or type? It's logical to have military base stationed on a barren rock, but it'd be better if it was logical in the game itself.
Is it? Air seems like a pretty good thing to have, even for military types

But, right - some industries are affected by planetary conditions. All industries are affected by the hazard rating of a planet; it increases their upkeep.
It would be nice if you expanded raid mechanic to make it usable for the player or factions in general (either as privateering or actual warfare), if you're affiliated.
Yep, it's something I'm thinking about.
Will Tiger Station and other freestanding stations remain as they are or become battlestations? Have I asked this before?
I don't think that's a vanilla thing?
In any case, something like say Kanta's Den:
1) remains a standalone station, and
2) has a (in this case) "star fortress" industry
Since the game is aware of the primary entity being a station, it doesn't spawn a separate "station" entity around it, but treats the primary entity as if it were the station, for purposes of combat etc. Hope that answers your question!
On the one hand I understand the implementation difficulties of allowing players to build stations wherever they want. On the other hand standalone stations in asteroid belts/fields and around gas giants are classic archetypes. On the third hand I've had fun playing semi-nomadic factions in other games and the concept of a planet-less faction is cool.
I hear you, but gotta draw the line somewhere. And mechanically, there's no real incentive to do that, except for rare cases where there isn't a planet at all. This is a "very, extremely unlikely maybe" in my book.