One simple question: if I choose devoted with Greatswords for example, and later I got another weapon that boosts my spells PL (Chromoprismatic Quarterstaff for example), my spells will have ACC penalty?

nope, but if you want to use Staff, then go with Staff devoted.

https://pillarsofeternity.fandom.com/wiki/The_Spine_of_Thicket_Green avaliable at Neketaka shop basically after like 30 minutes of play

Devoted only gets penalties when using weapons for which they lack training. So this includes everything aside from the weapon type you chose at char creation AND unarmed strikes; it's usually worthwhile to pick up monastic unarmed training so as to use fists as a backup when playing a Devoted build. Have you considered selecting pikes? Citzal's Spirit Lance is great with Clear Out. You can use fists to excellent effect until you can cast this spell. If you mainly want to cast spells and use stat stick weapons, you might consider going with warlock, for the nice barbarian speed boosts to casting. Battlemage is better, IMO, when you actually want to focus on magic enhanced melee. For this it's great. With Wall of Draining and Unbending you become virtually immortal.

4 hours ago, freddfranca said:

One simple question: if I choose devoted with Greatswords for example, and later I got another weapon that boosts my spells PL (Chromoprismatic Quarterstaff for example), my spells will have ACC penalty?

The Devoted's ACC malus doesn't affect spells, it only affects the attacks with weapons (without proficiency). Using the Chromoprismatic Staff to boost your spells doesn't turn tose spells into quarterstaff attacks.