I'm not understanding why trade anything for Lebron when he can opt-out and just sign as a free agent? Look for trades elsewhere for Garland and Mobley. I think we just keep Allen, we aren't landing a big name super-star without trading Mobley. I know it will be difficult with making it under the salary-cap but we know Dan Gilbert is willing to go into the luxury for a chance at a title!
Until we hear explicitly that LeBron will play for anything less than max money, we have to assume he's on a max contract. The Cavs will not have cap space to sign him to that in free agency. In the past, LeBron has made it known that he will not play for less than the max, primarily because it's a players union thing. Maybe that'll change, but until it does, it's unwise to expect.
If this is a sign and trade or an opt-in and trade, then Garland+LeVert either matches or gets close.
Personally, I'd want Mobley playing next to LeBron the same way I wanted Kyrie playing next to LeBron. It's an opportunity to learn from the very best. It's also widely-understood that LeBron is gonna give you very little defensively over the course of the season, so he needs elite defense next to him. I wonder if LeBron could play small forward any more at this stage in his career. If not, then maybe you consider moving one of the bigs so LeBron can play next to the other.
Pairing Mitchell with LeBron could be a ton of fun. I believe Mitchell would be able to carry the offense when LeBron sits in ways that Kyrie couldn't, particularly because Mitchell is one of the better kick-out passers in the league in his own right.
Cavs will need to find an abundance of shooters, however.