There are no rules for frame creation in the book. The frames were built by the devs according to a recent stream using the monster creation rules from the GM core not player character creation rules. Even a protoframe is as powerful as a 3rd level normal character and has their own unique abilities that are completely different from normal players. The module is meant to be played with the pregens.
There aren't any hard guidelines, but I could spitball a couple of things from browsing the pregens
-Try to include a warframes 1-3 abilities. They don't seem to have included ultimates- Having been away from warframe for a few years, I don't know if that's tied to how protoframes work or just to avoid handling how powerful many warframe's 4th abilities can be.
-The 3rd level protoframes (which a sidebar saying that the Devs reccomend using 4th level starfinder characters if you're bulking out the adventure) have one "advanced" weapon, although it can be a bit inconsistent which weapon it is. If you're designing a warframe or protoframe with multiple signature weapons (e.g. Gauss), I'd pick the most popular or iconic (definitely the acceltra in that case).
-All the warframes have vigourous swap to encourage switching weapons frequently.
-If you're building a warframe who would put a second "token" on the battle map, look to existing mechanics. For Khora, Venari would probably work similarly to an animal companion, while Wukong's clone is tricky, but I'd probably make it work something like a Thaumaturge's mirror implement.