I need a clarification on the intention of the two paragraphs involving similar/different abilities uner the Magic Item Gold Piece Value.
Multiple Similar Abilities: For items with multiple similar abilities that don’t take up space on a character’s body, use the following formula: Calculate the price of the single most costly ability, then add 75% of the value of the next most costly ability, plus 1/2 the value of any other abilities.
Multiple Different Abilities: Abilities such as an attack roll bonus or saving throw bonus and a spell-like function are not similar, and their values are simply added together to determine the cost. For items that take up a space on a character’s body, each additional power not only has no discount but instead has a 50% increase in price.
Now my question is, does similar mean "the abilities all affect the same general thing", ie. a +5 bonus acrobatics, and treat all falling damage as if all dice rolled a 1 and land on your feet, and wearer is under the effect of a continuous featherstep effect, able to ignore difficult terrain (basically combining boots of elvenkind, boots of the cat, and featherstep slippers)?
Or does it mean that all abilities you want to combine must be of the same general type, ie +5 to Acrobatics and a +5 to Stealth, a +2 armor bonus and a +2 natural armor bonus, etc?
I ask because this can have, potentially, a very big impact on a custom or combination items cost.
Per GM's decision. Custom magic items are almost always going to fail when thrown through the suggested formulas. I'd think the abilities you suggest for the three shoes are different abilities and fit the second situation. Skill bonuses, such as your second example, are similar abilities.
I'd consider AC related bonuses (bracers of armor, rings of protection, amulets of NA, etc), to be a different ability just like it calls out saving throw bonuses.
This however is simply my opinion as a GM.
Your best bet is to come up with the item and then sit down with your GM to price it. The best way to price an item is to compare it to other items that are already priced and be reasonable. Those tables are just a guideline for pricing and are sometimes way off compared to similar items.