[RPG] How to a caster cast personal spells on other creatures

1) Yes, you can.

The only exception are:

• Metamagic feats, you need the proper feat to craft each type of item.
• Spell Completion items, you need to know the spell to write a scroll.
• Spell Trigger, you need to know the spell contained in the wand or staff.

Everything else you can simply increase the DC by 5 points per requirement missing. Using your example, the Ring of Gate has a normal DC of 27 (10 + item's caster level, 17), if you know the gate spell. If you don't know the spell, or if you cant pay for someone to cast it every day spent crafting it, then you must increase the DC to 32.

2) You don't have to provide all requirements by yourself, you can get help from others. Example: a cleric could craft a Wings of Flying with the help of a wizard. But everyone helping you must be present every day spent crafting the item, otherwise the process must be started again.

That said, yes you can make any item, even if you don't meet the requirements, the increased DC means you have to take different approaches, research a different ingredient to replace the missing spell and stuff like that.

3) No, the caster level is the default DC for every item, it is also used to roll saving throws for unattended magic items, and to define the spellcraft DC to identify them (15+CL). To craft a Ring of Gate, all you need is enough spell ranks to beat the DC 32 check and have the Craft Wondrous Item feat.

The spell blood money creates a material component only for a spell the caster of blood money casts

The range of 0 ft. means the creature selects a crosshairs adjacent to its space and the effect of the spell happens there; the spell doesn't target a creature or an object. The spell's effect is to create the material component 0 ft. away.

This is, actually, a good capsule of the spell blood money's description, which says

You cast blood money just before casting another spell. As part of this spell's casting, you must cut one of your hands, releasing a stream of blood that causes you to take 1d6 points of damage. When you cast another spell in that same round, your blood transforms into one material component of your choice required by that second spell.

Thus, while casting the followup spell, the spell blood money creates adjacent to your space (presumably in your hands if you have them) the material component from the blood you spilled.

A creature can't cast the spell blood money on another creature; the spell's lack of a target entry prohibits it. This lack of a target, likewise, makes impossible a potion of blood money.

A command word activated custom item that casts blood money is a possibility, but the standard action to use a command word activated item makes casting spells involving the item problematic. A GM allowing a continuously active custom item of blood money should make such an item's price incredibly prohibitive, allowing, as it would, 0-gp castings of, for example, the spell wish.