[Starfinder] Looking for aid to convert Alchemist, Barbarian, and Ranger to SF.

[Arkhios]

I'm in the middle of a project to get ready to run a campaign using Starfinder as the rules system, and I'd like to add these class options from Pathfinder to the fold, before I have the session-0.

Alchemist with options to choose from Chirurgeon and Grenadier features.

Barbarian (Savage Technologist); I'd prefer to use Unchained barbarian as the base, even though Savage Technologist is made for standard Barbarian, so this probably requires a little more tinkering.

And Non-Spellcasting Ranger with Trapper and/or Skirmisher.

I'm a bit rusted with Pathfinder (I haven't played it for a couple of years), so I humbly ask your aid, if you wouldn't mind.

Thank you in advance!

The campaign starts with players "grounded" on a planet that has fairly classic post-apocalypse science-fiction elements. Solarian with its super-saiyan/jedi powers would be very out-of-place in there, so I decided it's not allowed. Likewise, for character themes, currently spacefarer is off limits, and likely Xenoseeker as well, because the characters are the planet's natives who have never set their foots into space, let alone other worlds. Their ancestors had managed to build orbital space-stations, but those are now inaccessible due to apocalyptic events that occurred in the past, and likely inhospitable due to centuries (or more) of neglect.

It's likely that roughly the first half of the campaign takes place on the surface of this planet, and the rest is more about space-travel.

[Morphic tide]

Well, an important note about differences between Pathfinder and Starfinder is that Starfinder has rather inflated numbers, so Barbarian's Rage needs to be offering a heck of a lot more damage than normal. Ironically, 3.5's Warlock is almost able to be used as a direct port with just the standard skill shifts and adding entries for Starfinder-exclusive stuff, because the damage scaling it has is pretty close to in line with what Starfinder expects.

More importantly, Starfinder is a science fantasy system, not pure science fiction. You've got technomancers powering freeze rays with magic and mystics channeling things from the Cthulhu mythos alongside people drawing power from astrological signs and robots powered by the collective unconscious. So spell-less Ranger is not needed, though the degree of casting is largely useless it still offers some important stuff to include in what the class can do.

Another important difference is that, for some reason, Starfinder decided to do away with CL scaling, so every Alchemist Extract that uses CL has to be rewritten to match Starfinder's number setup.

Off the top of my head, Alchemists should have bombs removed from their baseline (it renders the class a bit too messy for my liking) and moved to a set of Discoveries, with scaling being capped so you have to devote a significant amount of build resources to have viable damage. Discoveries should be the primary archetype trade, like Revelations for Solarians, and be where all the choices are at, save perhaps a choice at 1st level like the Engineer's choice between drone or integrated supertool.

Barbarian should have some Savage Technologist involved, enough for gear use, but most of that should be in the options list for the sake of being able to play a more magical/fantastic Barbarian, like a Totem Barbarian. Rage Powers should not be the only thing to enable this sort of tradeoff between magic and technology, but I'm not sure what to call the other sort. Or you could roll in the needed differences between magic-based and tech-based in a 1st level choice. Magic-based would be something like "I am covered in goddamn fire/lightning/whatever, therefor laser/bullet/axe is less effective and punch burns/shocks/whatever for added damage" to cover numbers, while tech-based would be something like "I have cracked/overloaded shield, therefor only some damage is blocked by it and the rest hits tough armor and my punch hits extra hard because buggy shield adds electrical/fire damage to it".

I... can't think of much for Ranger. It's just so outside of what Starfinder expects that I can't think of how to adapt it to science fiction. Starfinder is not an update of Pathfinder. It is a different system with different expectations, with different numbers expected of characters and more numbers to track. Conversion work can be simple, but if you want the conversion to fit in with the other classes, you have to do quite a lot to make it work in science fantasy.