End of Movie 3 (Freiza) Trunks shows up with the Z-Fighters and says, "Where's Goku?"
Then movie 4 is all Cell. I think it could work keeping him in one movie. I mean, as long as its interesting, a long movie could work if needed.
The prob is that the androids/cell saga does a double bluff that the other sagas don`t.
Piccilo saga is straightforward. Piccilo turns up, wants dragonballs, fights goku and is defeated.
Same for the saiyen saga. Raditz warns them. They train. Vegeta turns up. Wants dragonball. Fights goku and gets defeated.
And the frieza saga. They head to namek. Frieza is there. Frieza wants the dragonballs. He fights goku. He is defeated.
And the buu saga. Buu turns up, wants to wipe out universe (well kid buu does), fights goku and vegeta. Is defeated.
There is more meat to them than that but that is the basic structure. underlying the lengthy stories.
The prob with the android/cell saga is it includes a twist which is integral. The begining of the story features the androids as the threat and they evidently want to destroy goku. The plot progresses and then cell turns up as the real threat. He absorbs them and evolves. He fights gohan and is defeated.
It seems simple but lets keep in mind that fox loves 90 min movies. To have the whole android/cell saga in 90 mins you either have to...
a)have to cut a lot of the android story which would be annoying as the androids are very cool and to have them as just one-line fodder to be absorbed by cell would be a great diservice to the original source material. We would also miss out on vegeat getting his arm bust up which will be an undoubted highlight.
b) have cell only turn up at the end. Kinda like venom in sm-3. which undoubtably sucked. so that isn`t a good plan either.
the best way is to have mech-frieza turning up, getting diced by trunks, the whole warning about the androids, the hunt for gero, the death of gero, the first appearance of the androids, their hunt for goku and their fights with the z-fighters in the first movie. With an end of credits clip showing a larval cell crawling out of the beaten up time machine.
Then in the second movie you feature trunks and gohan finding the time pod, their discovery of the larval shell, the devastation caused by stage 1 cell, piccilo vs stage 1 cell w/ cell`s origin explained, cell`s escape, cell vs android 17, cell stage 2, cell vs vegeta and trunks, vegeta allows cell to absorb 18, third stage cell ie perfect cell, cell defeats vegeta, plans his cell games, cell games begin w/hercule (mr satan) included in some form for comic relief, cell vs goku, defeats goku, cell vs gohan and cells eventual defeat.
It also works out better as you would have a franchise pan out thusly...
Dragonball
Dragonball Z
Dragonball Z - Frieza Saga
Dragonball Z - Android Saga
Dragonball Z - Cell Saga
Dragonball Z - Buu Saga
So an nice double trilogy as opposed to just 5 films if you have androids and cell as one movie.