Ok seriously wtf @ the equipment and levelling system. Can someone explain a few things to me?
1.) What's the point of levelling up equipment and increasing proficiency? I'm taking it when you fuse some equipment and their skills are locked proficiency is how you unlock them? Is that the only purpose? Do two pieces of equipment with the same skill set but different proficiency levels produce different results?
If the skill is sealed, leveling the proficiency will unseal the skill. If the skill gets unsealed (or there was no seal to begin with), leveling proficiency just makes it cheaper to fuse that item (gald).
2.) So getting two horizontal skills of the same element is one way of getting a bonus skill. I read somewhere if you line up 3 that negates the damage reduction effect of lining up 2? Is this true and if so wtf?
Yes, it's true. It negates it and gives you a different bonus.
So, for example, getting a "stack" of a skill is getting that same skill multiple times. If you get a 2 stack (aka 2 of that skill), it reduces your stagger time by 6%. If you get a 4 stack, you get Ekseed, which increases your attack combo limit by 1. By going up to the 4 stack, you lose the 2 stack bonus, and going up to 5, you will lose that Ekseed bonus. It's not cumulative.
Generally speaking, the higher bonuses are better, but there are times where this is not the case and you will purposely want to avoid getting higher stacks. For example, I could get a 4 stack of A-ATK skill (Mynd) for that Ekseed, but if I get a 5 stack, I get a not so great skill called Aster. Aster makes it so the 10th, 20th, 30th, etc hit of your combo does extra damage, which I don't think is very good. In a case like that, I would rather avoid getting another one and aim to stay at 4, at least until I can get enough of the skill to get to a useful stack (7 for example, -1 BG cost on mystic artes)
This means I can't get another A-ATK skill (because I judge the Ekseed more worthwhile than that small A-ATK boost) right now, but I can get some other skills that would be useful as well. You can get multiple stacks, so for example, 4x of two different skills for two Ekseeds.
3.) How do you learn new artes? By constantly using them or by levelling up?
When your character levels up you can learn new artes. The order you learn them is dependent on the titles you are using, but you will ultimately learn them all.
4.) I read somewhere you increase your titles by levelling up. Is this true? So does that mean if you don't change your title from the beginning of the game you can effectively lock yourself out of levelling most of the titles because your level will be too high at the time to level up the titles you missed?
If you stay on a title that is max level, the others won't level up. However, if you like your title as is, that's not necessarily a bad thing. They all have different bonuses, but they still need to be equipped to get their benefits.