Started Playing The Last Remnant a couple of nights ago and I have been reading about grouping, leveling up, "classes", formations, selling creatures to get shops to open up other equipment and jesus christ:
And I work on three separate network IOS for a living.
I basically just played until I had a minor grasp on classes and developing arts and then just started over.
Selling creatures is far simpler than they make it sound on the wiki. You sell creatures to any shop and it increases whatever shops are interested in it. It doesn't matter what shop you sell to.
Unions is where most of the strategy in this game comes in to play. Some fights you want less overall unions with more characters in each (fights where enemies have high damage single target damage primarily) to give larger HP pools to absorb the single target damage. Some fights you want more overall unions with smaller character pools to lessen enemy AE damage. This is something you'll just have to see in action and observe because AE attacks don't always hit everyone in a union. Some spells have a small AE radius, some large, some are cone, etc and this is where formations come into play.
Classes are the first thing I would suggest getting a handle on. Classes work on a rank system. This means you can only change into a new class if that new class has a higher class rank than your current class. To change into a class you have to meet the class requirements as well. Take Assassin as an example:
Assassin - The Last Remnant Wiki - Characters, quests, walkthroughs, and more - Wikia
This is a rank 6 class, meaning once you change into it you cannot change into any other class unless that new class is a rank 7 class (of which there are only three, Ordainer, Warlock and Ninja). To change into Assassin your item art levels have to be higher overall than your mystic art levels, you need to have one handed skill at 15 and sword skill at 13. So to get Assassin you would need to:
1) Equip and use a 1 handed sword, making sure to use Combat Arts often and making sure your wield style is set to "one handed"
2) Have a character that has some Item Arts and make sure to use them more than you use Mystic Arts (to make it easier you can just make sure to never use Mystic Arts so you know Item Arts will always be higher until you get Assassin as your class)
The class system seems daunting at first but in reality it's very simple. Go to the wiki and look up the character you're interested in, see what abilities they can learn on PC (and when they learn them), then go to the classes page to see what suits them.
These two guides helped me when I was first starting. They aren't very good from a mastery perspective but are very good at getting you started:
The Last Remnant Class Guide for PC by Misfiring - GameFAQs
The Last Remnant Army Construction FAQ for PC by ShinesmanOW - GameFAQs
One tip that makes the game much more manageable early on. Once you have 1 or two characters who learn Vivification Herb (the Herb Item Art that resurrects a union or blacked out character) put those characters in their own separate unions and have them hang back and do nothing but heal and resurrect. Never engage. This way they never get attacked and killed and can just keep rezzing if your damage unions die.