The Idea of the rule stems from the Idea of the character.
The History and RP:
Think of an old movie or story with a strange person who dabbles in magic with a magic shop. When you ask to be able to do "_____" spell they grab a certain enchanted item, trinket, or potion. They dont have 12 - 14 of the same charms on the shelf. Each was made and crafted for a certain purpose OR the buyer had to come back later for the item when it was made.
What people forget is most rules are made so the Role Play of the character can be done like a myth or legend of a type of class. In this spirit you need two focuses (One for each set)
The Rules:
Implements:
You touched on them slightly with the question but here is the full set of rules
- One item/implement for the spell learned that day
Every day, the occultist selects one item from that school's list to be his implement for the day for each implement school he knows.
- Multiple Items/implements
The occultist needs only one such item to cast spells of the corresponding school, unless he selected that implement school multiple times, in which case he needs one item for each set of spells gained from that school
What this does is allow the character to have the extra spell slot at the casters level. Without the implement the casters spell is minimum level for the spell to be cast (EX: 2nd level spell needs 3rd level to cast so it will be 3rd )
If the occultist lacks the corresponding implement, he can attempt to cast the spell, but must succeed at a concentration check (DC = 20 + the spell's level) to do so.
So you are allowed those spells with the items/implements. You will have to choose for each spell ....
Every day, the occultist selects one item from that school's list to be his implement for the day for each implement school he knows.
an item and at that point have access to both spells even if same school...
The occultist needs only one such item to cast spells of the corresponding school, unless he selected that implement school multiple times
Focuses:
These are easy and pretty well written once you know how many items you are suppose to have which was the main question but for the "TLDR"s
Once mental focus is invested inside an implement, the implement gains the resonant power of its implement school
Meaning each implement needs to be focused on to cast the spell without penalties....like the Movies :)
TLDR for the final question set:
So, if I take extra transmutation spells, I need two transmutation items--
Yes
does that count as to transmutation implements?--
Yes
Can I invest mental focus in both separately--
Yes
and get two of my stats buffed?--
Yes
Or do both items count as a single "implement" for the focus ability?--
No
Do I just need multiple items--
Yes
but still just pick one of them each day--
No.. both are needed if you want the extra spells for each implement
Hope this helps.