Help setting up dual boot on laptop

Need some help, but stick with me cause it's kind of a long story.
So, I'm trying to set up my Acer Aspire V5 laptop to dual boot between Windows 10 and Ubuntu Gnome 16.10
To start from fresh, I backed up all my stuff. Then completely re-installed Windows 10.
My plan was to set up 3 partitions on my 500 GB hard drive: an 80 GB partition with Windows installed on it. A 50 GB partition with Ubuntu installed. And the rest of the drive as common storage for both operating systems.
After re-installing Windows, I went into the UEFI and changed my boot order to to my disk drive before Windows Boot Manager, but when I restarted my laptop it just went right back into Windows. I checked the boot order and it reset back to the way it was before. My laptop wont allow me to press f12 or something at startup to go into the boot menu. The option isnt even there.
I tried a few things. Someone at the LTT forums suggested I disable secure boot, but that changed nothing. Then someone else suggested I change the boot mode to legacy BIOS mode. That allowed it to boot from the CD. But before I installed Ubuntu I wanted to go back into Windows and set up your partitions first. But because of the legacy boot mode, I couldn't get back into windows. So I cleared CMOS and got back in. And now I'm back at square one with just a fresh install of Windows 10.
So after that long story, could anyone help me set this up so I can choose which OS to use on startup and have my 3 partitions configured?

You're overcomplicating it.
1: Install windows, create the partitions
2: Enable legacy bios
3: Boot the live usb/disc
4: Install linux on the reserved partition - make sure there's a tick in a box if a popup asks to overwrite a bootloader.

So when you boot grub will display options if you want to boot into win or linux.

No I like it I want to see him make it nuclear.

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Actually trying to share partitions is already needless unless you really need a ton of storage and must constantly access the same files from both environments. (From linux you can access the win partition btw).

So it would just be easier to
1: Install win
2: enable legacy bios
3: Boot the live usb/disc and "Install ubuntu alongside windows", say 300 gigs for win, 200 for linux.

I thought about just doing this but the install disk doesn't detect that Windows is even there. It doesn't give the option to install alongside

Fair enough, you can shrink the win partition from the install disc too, and just install linux on the empty part.
Esit: did you make sure you actually shut down w10? Since it by default basically just hibernates.

If by that you mean disable fast startup, then yes I did

Idk if it's the same thing, but from the cmd (as admin
'shutdown /s /f /t 0'

Alright I'll give that a try tomorrow. Left my laptop at work (repair shop) overnight cause I coudnt be bothered to put it back together after digging for the cmos battery. Thanks for the help so far