Data backup advice

Hello! I am trying to help my fiance with her data storage which has become a mess. Her iCloud is full, mostly with a data backup from her phone + photos, her iphone hard drive is full, mostly with photos. She does not want to upgrade her icloud size because she has a huge dropbox for most of her file storage, but also is concerned about backing up dropbox too. Just picked up a 12Tb Drive (seagate expansion) and here is what I'm trying to do, and I'm seeing a lot of warnings all over previous message boards that are giving me some headaches. I'm wondering if there is a logical order on how to do all of this or any advice on these goals: 1. Backup the macbook pro: I'm wanting to use time machine but since I'm also planning to do #2 and #3 below I'm seeing some comments that this isn't compatible (can't have time machine set up AND backup dropbox to the hard drive??), but can this be fixed by just partitioning the drive and/or setting up a limit to the time machine size? 2. backup the iphone directly to the external drive, which I have seen some videos explaining how to link backup folders and "trick" your OS to do this. But is there a better way? Should I just backup the phone to the computer before doing #1? 3. Back up from dropbox to the external hard drive (she has her reasons to do this) 4. Delete the phone backup from icloud, clean up her icloud storage and make sure all photos are backed up to drop box 5. move all photos to dropbox and set up automatic backup there 6. re-backup the phone to icloud and stop backing up photos Thank you for any and all advice that you can provide, thank you!