First off, I think FnF should be the first saga of the anime, not a movie. Maybe we get a very short (3 episodes at MOST) recap of BoGs, but then it's all new material. That way we can get episodes detailing Goku and Vegeta's training and juxtapose it with Freeza's own hellish training. I think the segment with Goku and Vegeta training should also make clear the two base theory is a thing so God level won't become instant fodder anyone can reach.
I don't really mind Freeza being revived in pieces, and in fact I like that a lot. It's not the first time the dragon acts like a dick for no reason (Remember when Piccolo was brought to a random landscape on Namek?). Like CC says, Freeza's own torment in Hell only contributed to make him stronger, and even gives him the idea to train and get even stronger. Freeza training in the Demon Realm is a great idea by CC that makes use of this long forgotten corner of the lore. I like the concepts Kenshi and CC bring up with Tagoma being Cold's top goon and a rival to 2nd form Freeza and Shisami being a cyborg, though I could also see Shisami being from the Demon Realm given his appearance.
Roshi tagging along for some action isn't really bad, but Yamcha (and maybe Chaozu) have to be there too for it to make sense. Why allow the old mang to come but not those two? Goten, Trunks and 18 also have no reason to stay behind. Since Goku and Vegeta are absurdly strong I see no reason to give Gohan AIDS, and in fact it avoids yet another repetition of his character arc for the ToP.
I see no reason for Tagoma and Shisami to even survive into the third act. They get in a 4 way battle with Gohan and Gotenks where Tagoma is clearly the weakest link, giving Ginyu an oportunity to snatch his body when Gotenks knocks him on his ass. What can I say? Ginyu is a great character and Vegeta deserves that kill. Like CC says, Tagoma being from Ginyu's original race allows Ginyu to use Tagoma's body better than him. When Freeza loses patience and uses his Death Beam to kill the Saiyans, it's his Ki that grabs Goku and Vegeta's attention and allows them to use Shunkan Ido.
Freeza blasted clean through Shisami to get to Gotenks, horrifying even Ginyu for treating his own men like that. Luckily the boys defused, but now they're even easier targets for Freeza. Gohan jumps in front of Freeza's death beam to protect his brother and dies. I think this is a sacrifice much better than Piccolo's because Gohan has only died once before and it was off screen. Everyone is shocked, Trunks can barely hold Gohan from charging Freeza. When Freeza is about to blast them... Goku and Vegeta arrive and block the blast. Goku is angry at Gohan’s death and Vegeta lets him have the first round. Freeza tells his hundreds of goons to charge them and Goku blows them all away with a Kiai. Ginyu is the only one alive, and Vegeta vaporizes him.
The final battle starts. Base Goku vs 4th form Freeza, and then SSJB Goku vs Golden Freeza, just like the movie. Both Blue and Golden are extremely draining forms (so this won't come out of nowhere later), and after Freeza is exhausted Goku reveals he knew he was outmatched and didn't bother going all out to conserve stamina. Goku brutalizes Freeza, Sorbet (who wasn't wiped by Goku earlier because he wasn't fighting) comes to the rescue but his laser barely stings Goku. It does give Freeza an opening to blast Goku through the chest though. Goku is down for the count, it's Vegeta turn now.
At this point I think dragging Vegeta vs Freeza will do more harm than good. Freeza does get some upperhand thanks to a stolen senzu or magic healing capsules, but a healed Goku and everyone else distracting Freeza is enough for a Kamehameha + Final Flash combo to vaporize Freeza. There's the scene with Whis saying they should've teamed up and Goku and Vegeta saying "nah", and the saga ends with the other villains welcoming Freeza back in HFIL. The end.
