From what I can see, you don't need to be a full caster, just something that gives you a cast spell ability. For example, the rogue minor magic. As long as it does not turn into a 'innate spell' or something like that.
The only rules I found was on activating a item where it talks about if it says cast a spell, you need a spell caster ability to 'cast a spell'. All of this is purely off my memory.
I'm wondering how a rogue could activate a scroll, or a fighter a wand. Is it just going MC or am I right and anything that gives you some sort of casting ability that is not just a innate spell gives access to scrolls and wands? (not staves since they have their own rules for regenerating spell points) Does this also mean that you can use a 10th level scroll at level 1? I'm sure I missed something and someone here will be able to quickly point me in the right direction.
a "spell caster" in this edition isn't just anyone who casts spells:
"spellcaster A spellcaster is a character whose class or archetype grants them the
spellcasting class feature. The ability to cast focus spells or innate spells does not
by itself make a character a spellcaster."
so you specifically need the "spellcasting" ability, which i think it's only via MC for a rogue
If you are talking about the Rogue Minor Magic feat, it does not give the Cast a Spell activity. Since it does not give that, I do not believe it allows the rogue to use a scroll, wand or staff.
The Trick Magic Item feat along with the appropriate knowledge should make it possible to use those items based on a skill check. It is the closest thing I can find in this edition to the Use Magic Device skill from first edition.
The Multiclass Dedications give the Cast a Spell activity and therefore should allow activation of a scroll, wand or staff. Strangely enough, as best I can determine only the staff has the limitation of being able to cast a spell of the level in order to activate it. It appears to me the Dedication feat is enough that (assuming you have the correct tradition) you can use a wand or scroll without fail.
My reading on it thus far would be that any MC caster would be able to use a wand or scroll of any level, but the save DC and spell roll information would be set by their level.
basic archetypes give you "trained proficiency in spellcasting" so yeah, it would be level+2 for save DC and attack rolls if you don't pick any other feats.
MCs also set the primary score for your spellcasting as well.