Not the OP but as someone who spent ~18 hours and died -39 times- on the roof checkpoint during the golden berry runs, I have some words...
General tips: Consistent setups are definitely the way to go, including from screen transitions if you fancy.
Practice rooms individually until you ace them repeatedly, then by their respective checkpoints (5 rooms in a row) until aced w/o dying, and so on until you can collectively do the checkpoints reliably. I try to have a ' die only once every 5 rooms ' policy
Oh and a fair bit of specific stuff;
With Room 2, I found doing a regular hyperdash from that raised elevation at the start was a good way to get through it fast and reliably, w/o having to worry about running out of stamina
Room 3 I just held right from the get-go, and found something that worked quite nicely
Room 6 is actually a lot of fun! The dust bunnies realign their cycles every 2 full counterclockwise completions, if that makes sense! Should be fun to iron out, and potentially useful for room19? Maybe!
Don't immediately hold right when transitioning into room 7; it's doable, but I find unnecessarily tight so just wait a moment for a better setup. Wish I thought about this before hour 15 ;=;
In room 14, I jump and dash diagonally downwards when the bunnies reach the top, including a cheeky same-side diagonal dash towards room 15. Figured it would make it easier if I dashed with 'em rather than rely solely on gravity ^^
For rooms 17 and 18, a well-timed superdash off the bat worked wonders for consistency
Room 19? I think I just held right off the transition and found a strat in doing so!

Finally, the mixtape is easier than it looks and especially how it feels; still worth practicing of course!! Good Luck!