So, I've now completed the main story. SS3 Goku VS Pure Boo was a little tough, though the other three boss fights at the end as Vegeta twice and Base Galu at the end were surprisingly easy aside from Pure Boo using the candy beam. I found the boss fight against Majin Vegeta more difficult, though I'm surprised to say the third most difficult boss of the Boo Arc was...Yakon.
Now going to focus on finding the Dragon Balls, doing sub-stories and levelling up before taking on Mira. Currently, my character levels are:
Goku - Level 74
Gohan - Level 81
Vegeta - Level 74
Piccolo - Level 49
From what I've heard, you can play as Trunks again once doing certain tasks (of which I imagine involve going to Capsule Corp.) and I've heard you can replay past levels in case you missed any of the sub-stories. Hopefully, levels remain the same rather than being reset as that'd make a pretty good way of grinding for EXP.
After investing so much time into the game, I can definitely say it's quickly become my favourite Dragon Ball game. It's not without its flaws though in terms of conveying parts of the story and certain additions definitely clash with established canon such as some side quests (mainly those with the Pilaf gang) or the encyclopedia entry of seemingly trying to retcon Piccolo's moon bust into being him creating an illusion of the moon disappearing which makes no sense, but I'd say it places more effort into telling the DB story in a way few other games of the franchise even come close to. The combat isn't the best as it lacks the complexity of BT3's customisation or the fluidity of Raging Blast 2, but if looking at it as refining Xenoverse's formula, it does so to a nigh-infinite degree.