I will have martial weapon proficiency, its not like I will have no training at all in throwing stuff....
To be honest using playing cards as improvised weapons is already supported but you get a -4 nonproficiency penalty... That said you are supposed to compare relative size and damage potential to the pre existing weapons, Shuriken are about the right size but would obviously hurt more (and they deal 1d2 damage) so playing cards would probably deal less than 1 damage (but it rounds up to 1 anyway).
As far as adaptation goes, I generally just remove racial prereqs for being a stupid idea when I'm DMing. Though your game your rules obviously.
Build, Providing rune smith is ok and i dont find another 3/4 BaB class with casting to take over from spellwarp sniper (because at the minute I have to use 2 feats to get sneak attack) :
[spoiler]
1. Wizard 1/Fighter 1
2. Human Paragon 1
3. Wizard 2
4. Human Paragon 2
5. Wizard 3
6. Runesmith 1
7. Spellwarp Sniper 1
8. Arcane Archer 1
9. Arcane Archer 2
10. Arcane Archer 3
11. Arcane Archer 4
12. Arcane Archer 5
13. Arcane Archer 6
14. Arcane Archer 7
15. Arcane Archer 8
16. Arcane Archer 9
17. Arcane Archer 10
18. Abjurant Champion 1
19. Abjurant Champion 2
20. Abjurant Champion 3
[/spoiler]