Thanks to all of you for the support. And thanks, Chris, for reassuring me it CAN get better! A little hope goes a long way.
We are on day 4 of separation. Lotto is nearly back to his old self. He does have fleeting moments of anxiety, but he's exploring, interacting, purring, and even playing with me more. His only irritation is being shut out of the rest of the house for the majority of the time. I go in there at least 5 or 6 times a day, and we try to put Bucky in a guest room once a day for a couple of hours so the other cats can wander around the house - but Lotto is smart enough to know and realize that his house has been 'taken' from him. He keeps going to the two different doors that lead to the living room and trying to open them. We have a 'secure fortress' set up with a montage bungee cords and hand weights keeping the doors shut LOL That being said, the other two cats are safe, and are even getting along with each other again.
Bucky is even a new cat - he's more friendly, lovey, vocal

, and more relaxed. He gets very upset when I go in the other room with the other cats, though - he will sit at the door and cry cry cry. My husband is trying to get more involved with him, and has been doing a decent job of playing. But it's so amazing the kind of change he's gone through just from being separated. He shows NO signs of aggression whatsoever.
We've added a lot of the things Marilyn suggested....our only issue seems to be with the litter boxes. We have 2 litter robots, and have loved them for about 5 or 6 years now without any issues - even with Bucky. Even though Lotto is a little longer than the box, he can put his head and front paws out of the box and be perfectly comfortable. But Marilyn said she does not like litter robots, and that we needed to change to different litter boxes. So I 'created' a litter box setup made of the clear tote bins.....My problem is that Lotto still wants to go in the litter robot, and just wants to 'play' in the litter in the new litter box.

Of course, it is a minor issue, and I can always leave one litter robot in the house while the others use the bins.
Question for you guys....it occurred to me that with them being separated, that reintroduction could go either way. For instance, they could figure they have adequate resources, and live in peace. OR, Bucky could get used to having most of the house to himself, and us when we are working in the living room, and reintroductions might go the opposite way with him being more territorial.
Has anyone had a new kitty not work out - where they just needed to be an only cat? I worry about Bucky - I have no reason to think this won't work, but something in my gut is nervous that he seems to be enjoying being separated so much.
Or perhaps I am just paranoid.....regardless, everyone seems a little more happy at least....and for that, I am grateful!
L