Questions regarding Diminutive Size and some other, kind of random questions

[Erroangelos]

Hello friends! My friend is starting a custom campaign wherein he wants us to all use really weird if not outright custom races, after some discussion with him we figured I could build a race similar to the Atomie from Bestiary 3 and run some form of an Arcane Trickster / Ranged Sneak Attacker.

The issues we have been encountering regard the Diminutive size of the Atomie, we are extrapolating that the size modifiers are as follows:

1. +4 AC, +4 Attack, -4 CMB, +6 Fly, +12 Stealth, -6 Str, +6 Dex

Is the above correct for the Diminutive size?

2. The item weight modifier for this size, we think that it decreases by 1/2 per size modifier making Diminutive a 0.125 modifier (1lb = 0.125lb) however we have encountered other charts saying something closer to 1/10 weight. (We originally thought keep dividing by 1/2 because small creatures weight is 1/2 and assumed that as size kept going down another 1/2 was added)

2a. Does the size modifier for an item for a small creature such as this effect the cost? How are special materials like mithral/adamantine effected?

The last set of questions have to do with the fey type on the Atomie from bestiary, is the fey type giving them just low-light vision according to http://www.d20pfsrd.com/bestiary/rules-for-monsters/creature-types#TOC-Fey
or does the Atomie follow a template for fey, http://www.d20pfsrd.com/bestiary/monster-listings/templates/fey-creature-cr -1-or-2 (according to the custom race guide, spending 8 rp to get flight means they should have 50ft, average but they have 50ft, good according to that template)

Other minor questions involve:

For a diminutive size longbow, is the range increment effected by the size changes?

Since a creature that small cannot flank, can sneak attack even benefit from something like the gang up feat or would it have too focus on sniping through stealth or greater invisibility from arcane trickster

I guess it might be easier if someone can come up with a complete list of things the Atomie race would have, if anyone wants to be that nice to help us out - we've never really tried going this small before.

Thanks!

[avr]

1. Looks right. Note that CMB will be based off Dex not Str as well, likewise the climb and swim skills if those come up.

2. I'm pretty sure the 1/10 weight was someone's approximation for convenience.

2a. Cost is usually the same, though armor has half cost and half the armor bonus. Whether that cost multiplier applies to special materials is undefined in the rules.

The atomie as a monster was created before the template and would not use it.

By RAW range increments are not affected.

Yup, be sneaky or invisible.

[Erroangelos]

@Avr

Thanks for the reply! Glad to see we didn't like completely mess up.

It was a little confusing with the special materials part because Mithral states 500g/lb for "other items" with the example being a dagger which would imply cost per pound of mithral used, yet it lists a flat rate for armor. I suppose it could be explained by saying that the price reduction for needing roughly 1/10th the mithral is countered by how hard it would be for a smith to craft such a tiny piece of armor expertly making the final product still cost the same.

I was kind of hoping there was an official statement - somewhere - that we just couldn't find