[RPG] Armor’s effect on skills

So, a couple things.

An arcane spellcaster suffers from the listed spell failure chance while casting spells - but only those that have somatic components; see Arcane Spells and Armor in the SRD.

Anyone wearing armor takes the Armor Check Penalty to all STR and DEX based skill rolls. However, nonproficient characters (like your sorcerer) also take that penalty to attack rolls and all skill checks involving moving, see Armor Check Penalty and Light Armor Proficiency in the SRD. But yes, in this case the penalty is 0. You could go up to leather with an ACP of 0, though you do go to 10% spell failure.

Of course, if you choose a sorcerer build that has a lot of non-somatic spells and spells that don't require hit rolls, you're good with even heavier armor. This is likely to be a very low level workaround as that armor won't stack with Mage Armor, Bracers of Armor, or all the other tricks most mage types use to have a decent AC.

Your animal companion, like any other creature, can attempt to use any skill that does not specifically forbid its use without training, and does so just as any other creature does. However, its ability to do so may be restricted by its lack of training (such as in the case of Knowledge skills), and/or its lack of ability to communicate (such as in the case of Diplomacy). As well, there may be circumstance bonuses or penalties (there's a section on those in the core books) that apply, and I'd consider it highly likely that your DM may choose to make house rules about skills such as Craft, Spellcraft, etc.

For all future reference, the above considerations apply to anything with hit dice - they can try to use any skill that they're not specifically forbidden from using by either training or a creature trait (such as Mindless).