Congrats on Terra!! If you have Yangs LD and Cor I highly recommend them to play team whack everything on its ass with her.
Cor is basically use his s1 or s2 on Terra, have her go into LD or BT and he'll attack every time she does his.S1.and.S2 allows him to attack the enemy the characters has chosen before they do their own attack and it works on bursts so you can essentially have huge damage output.
His own LD gives him access to Reaper's Gale which ignores defence, buffs etc so he hits for max damage which is really useful in brave reduction fights. Also his S1 and S2 prevent the character he chooses being broken for 6 turns, he's just bonkers and extremely broken.
Noctis, his LD board give him some extra attacks and brave refund but now i've used him he's ok but he needs his rework which doesn't come until his BT+ so he's fine but still not on par with other units
I used Noctis for a long time in the earlier BT era so quite familiar with his kit.
He's all about turn manipulation which happens when he attacks a broken enemy and moves his turns up to before theirs when his S1 and 2 are in + mode so he's best used when his s1 and s2 hit their + versions as he also does follow up attacks. He's not a straight up damage dealer he lacks in damage compared to others now but he packs a punch thanks to manipulation and can hold back enemy turns and his ex provides him with free turns as well which is incredibly useful.
He's best to use with characters that can buff him as he does need support to get full damage, Rosa and Reno are excellent synergy with him during the Equinox event.
His LD changes his HP+ to HP++ and gives him his point blank warp status so he follows up on HP attacks.
For his burst my rotation is usually AA before the burst to open up all his + attacks including his Ex then select his burst and go Ex+, LD, S1+, S2+ HP++ Burst.
His Burst effect, he follows up everytime another character attacks so say you bursted with him and then used Terra and her LD he'll follow up after every attack she does.
But If you want to see the best way to use him then use
https://www.tonberrytroupe.com/home
They have amazing info on every character, how to use them, rotations, spheres that are best for them, playstyles advice on Lufenias, Dimensions End, i'd be lost without them.
Shantotto I've no idea really about using her and I don't really plan to, I don't like her, i've two of her burst both from multi banners this one and a past one but I'm not going for her LD and I have no plans to utilise her.