I cannot stress enough the importance of the initial character concept. Keep in mind that your character is a human, and most likely doesn't know the "true" nature of the world, or of magic and Nephilim at least. Remember that humans really aren't the focus of the game; the Nephilim quest for enlightenment is currently all that's published in the books. But also keep in mind that since this human has "graduated" to character status, she is an exceptional being. Really powerful psychic power should be a rare thing in the game world, and the character may be painfully aware of that: perhaps she's being chased by governments (enlisting) and scientists (dissection) and secret societies (elixirs? or maybe something worse...) that want to tap into their power; maybe she's an outcast in the "normal" world, shunned by people who are afraid of her powers.
Whatever the concept, keep in mind that the character is not necessarily framed by her psychic abilities, and should not be centered around them (unless it's part of the concept, of course, like a Tibetan mystic? Or a gypsy fortune teller?).
Also, needless to say, all rules for Nephilim and their simulacra apply to human characters - damage, combat, and everything else holds true for plain vanilla humans. Skills are learned in the same manner, and it's really advisable to hold with the "less than 90% in a skill" adage, as skills developed in excess of 100% are really the result of several lifetimes of advancement, whereas your human obviously only has the one lifetime of experience.
A quick summary of character generation for those who don't have it handy: INT = 2d6+6, all other abilities 3d6. Roll 1d4+6 to determine number of Profession-related skills, multiply INT by 15 to determine the number of percentage points in those skills. Distribute 3d6 X 10 points among other skills however you want. And of course, examine the sample simulacra for ideas, etc.
Player Name: Joe Q. Roleplayer Character Name: John Smith, 008 Profession: Super-spy, Her Majesty's Secret Service Age: 32 Ht.: 175 Wt.: 6'1" Sex: Male Social Status: 11 Opportunity: 33% (w/access to special resources) Education: 17 Life Experience: 75% Family Relationship: 3 Appearance: Very dapper, English, well cropped brown hair. Answers to "Smith. John Smith." Solar-Ka: KA : 17 Vision: 54% Abilities: STR: 10 Effort: 30% CON: 11 Resist.: 33% INT: 16 Idea: 48% DEX: 12 Agility: 36% CHA: 15 Persuade: 45% Attributes: Actions: 3 Damage Bonus: none Body Armor: 3/5 (para bullet vest-tuxedo) Aura: 11 Hit Points: 11 Possessions: lockpicks, infrared goggles, sniper rifle, tuxedo, scuba gear, watch w/built-in laser, exploding toothpaste, license to kill. Skills: Weapons: Handgun 75%, Heavy Weapon 35%, Kick 70%, Rifle 80%, Shotgun 65%, Submachine Gun 75%, Fist/Punch 80% General: Scan 65%, Pilot 45%, Scrutinize 70%, Survival 90%, Hide 85%, Hunt 50%, Listen 60%, Conceal 55%, Climb 70%, Drive 65%, Dodge 80%, Taste 90% Psychic Powers: Primary Sphere: MIND Secondary Sphere: SPACE Psychic Skill Modifiers: MIND: Charm +13%, Empathy +15%, Confuse +20%, Telepathy +10%, Invisibility +15%, Mind Reading +17%, Mind Control +10% SPACE: Spatial Reading +20%, Clairvoyance +20%, Clairaudience +15%, Mirror Image +10%, Expand Space +10% TIME: Premonition +10%, Divining +15%, Chronal Shield +15%, Speed +10% MATTER: Psychokinesis +15%, Psychopyresis +10%
Also, one psychic can teach another their skills - a psychic who has a greater skill modifier in a power can teach another psychic up to their level - as long as a psychic regularly studies under a teacher, the points received after a successful casting are increased by +1% for each +10% greater ability the teacher has in that power rounded down.
Example:
Bob has +22% in Temporal Reading. He is being taught by the Master Yee Fong to improve his Time abilities - Master Fong has a +55% modifier in Temporal Reading. When Bob identifies the age of the Master's amulet correctly, he gains a +3% to that skill, finally giving him control of the Time Sphere.
In general, I think that this is a pretty fair system - I tried to build in some rationality with the numbers - some of the modifiers to powers I suggested were based on my own ideas of what psychic strength in my world would be, according to how I feel psychic power is represented in my campaign. But, in general, I think a good rule for determining difficulty potentials is:
150% of Ka = Nigh Impossible Difficulty Task - or, 15 Ka has a "nigh impossible difficulty potential" of 23.
That gives players in general a 1 in 4 chance of completing the action, which seems right for impossible actions in an RPG; and anyway, this is not what the chance would be in either of the opposing spheres - there it would be 1 in 8 or 1 in 10, depending on their modifiers. Go with the task potential chart in the Gamemaster's Veil, and you should be able to wing it. Hard difficulty tasks would probably about equal kaX2, but depending on how strong you want humans in your campaign, that should be adjusted (i.e. is it "normal" in your world for humans to throw people around with their mind, or just bend spoons?). Again, play with the thought in mind that your human players are going to want to have just as much fun as your Nephilim players, but that humans in general should not come anywhere near the power levels of your average Nephilim.
Also remember that Nephilim believe in the Axis of the solar system, and it is this Axis that formed the guide for the Sun, which in turn beams the forces of the universe through the prisms of the planets, congealing into the magic fields on Earth (pg. 11-12). Also Nephilim only concern themselves with seven of the celestial bodies in this system - yet there are more. Nephilim also claim that the opposing interaction between sun and moon sparked life on the planet, initially creating the moon-based Saurians.
And, as for human/Nephilim relationships - here are some examples of Arcana that may or may not be linked to solar-ka magics, and some quotes that explain why they may be opposed to or encouraging of them:
Arcanum I: The Magician - "The Nephilim of this arcana work closely with certain human beings who study the mysteries of Nephilim magic and the Solar-ka."
*Arcanum XII: The Hanged Man - SEE BELOW
Arcanum XIII: The Unnamed Arcanum - The Selenim
Arcanum XVI: The Tower - "They also try to prevent and suppress the spread of occult knowledge among humans by killing anyone with obvious occult knowledge or high Solar-ka... They are the direct rivals of the Magician."
Arcanum XIX: The Sun - "These Nephilim study the powers of the Sun. They are the most mystical of all. They look for ways of accessing and using the eventual magic streams of the sixth ka, the Solar-ka."
*Using this arcanum is probably the best way to incorporate solar magic into your game world if you're reluctant to give these powers to human PCs or NPCs. This arcanum is best described as Nephilim-who-deny-they-are-Nephilim by trying to live exactly as their simulacra would and voluntarily throwing themselves into shouit. The book recommends against playing this kind of character, calling it "difficult and perverse", but if you're really, really against giving humans magic and still want to play with these rules, you can try and work something out with this form of Nephilim - maybe in the way that the unsuppressed human starts discovering that he has these neat powers when the Nephilim is in shouit, or something... Anyway, the Nephilim Mailing List is currently hashing it out. There should be a thread for it on the Nephilim Mailing List Archive.