[RPG] Craft A Wand of Fireball at CL 4

First question: trigger

The character needs only to have at least one level of a class which can cast the spell. In this case a first level wizard will be able to trigger any wizard spell.

Second question: completion

From the SRD: Scrolls

To have any chance of activating a scroll spell, the scroll user must meet the following requirements.

• The spell must be of the correct type (arcane or divine). Arcane spellcasters (wizards, sorcerers, and bards) can only use scrolls containing arcane spells, and divine spellcasters (clerics, druids, paladins, and rangers) can only use scrolls containing divine spells. (The type of scroll a character creates is also determined by his class.)
• The user must have the spell on her class list.
• The user must have the requisite ability score. If the user meets all the requirements noted above, and her caster level is at least equal to the spell's caster level, she can automatically activate the spell without a check.

This means that the character must be a spell caster of the correct type (arcane or divine): so no a fighter will not be able to use a scroll.

If she meets all three requirements but her own caster level is lower than the scroll spell's caster level, then she has to make a caster level check (DC = scroll's caster level + 1) to cast the spell successfully.

In this case: yes a first level wizard will be able to try with any arcane scroll (if he has the required Int) but he will have to perform an appropriate caster level with the following consequences:

If she fails, she must make a DC 5 Wisdom check to avoid a mishap (see Scroll Mishaps). A natural roll of 1 always fails, whatever the modifiers. Activating a scroll is a standard action (or the spell's casting time, whichever is longer) and it provokes attacks of opportunity exactly as casting a spell does.

Use magic device

You can use this skill to read a spell or to activate a magic item. Use Magic Device lets you use a magic item as if you had the spell ability or class features of another class, as if you were a different race, or as if you were of a different alignment.

This allow to override the first condition: even if you are not of the correct class (or have the wrong alignment and so on) and you have the use magic device skill you can do a check and try anyway.

So in this case if your 20th level fighter is trained in use magic device: yes he can use a scroll

It is reasonable that this character can 'take 10' for a roll

Yes you can always take 10 when not in combat or your life is not in danger.

Are all of these calculations correct?

They seem to be in order.

Does a +4 or +6 item just costing more money and time? (same CL)

In the case of belts / headbands, this seems to be the case. Note that Weapons and Armor have different rules (3x modifier).

Can I use a scroll? Can I use a Wizard friend?

Take a look at the Cooperative Crafting text here. The basic answer is yes.

The details are:

1. They must be present for the whole time.
2. They are casting that spell each day during the process.
3. If they are an NPC, they are charging each day.

Clearly if you wanted to do this with scrolls, you could, but you would need to expend the scroll every day you are crafting. At 150gp * 4 days, that's pretty expensive.

Does that make the earliest level for a non caster 7 to craft magical items?

• There are classes with odd bonus feat progressions such that you could get two feats at level 5 and spend them both. For example, the Psychic Warrior has this.
• I guess you could also "not take" a feat at 3rd level and then spend them both at 5th level. I'm not sure if there are explicit prohibitions against this.
• There's also the concept of "re-training" of feats as allowed by some DMs (see comments)
• In general 7th level is the minimum for magical crafting without magical crafting abilities.