Installing Ubuntu Linux 16.04 alongside Windows 10 on secondary hard disk

I would like to install Ubuntu 16.04 on a Dell Inspiron 7570. It has a 256G SSD and 1TB HDD with Windows 10 installed on the SSD. I partitioned the 1TB HDD to create ~500GB space for a potential Linux installation (using Windows Disk Management, which now shows this space as unallocated), the rest is being used by Windows 10 for my Windows data.

Now I want to install Ubuntu 16.04 on this 500GB space, but am not sure how I should be going about the partitioning and bootloader business - esp. reading a few articles on the web is leaving me a bit confused including would it be Windows Boot Manager or GRUB that would start the system? When I started the Ubuntu installation I got a message asking if I wanted to install 3rd party hardware drivers to which I said Yes (it has a NVIDIA GEForce 940MX Card), so it asked me for a password to disable secure boot which I gave.

Please see the screenshots below which indicate the way system is partitioned. Also the device for bootloader installation drop-down in the screens below has the following options:

/dev/sdb ATA Micron 1100 SATA (256GB) ---->SSD
/dev/sda ATA ST1000LM035-1RK1 (1.0TB) -----> HDD
/dev/sdb1 - Windows Boot Manager
/dev/sdb4
/dev/sdb5
/dev/sdb6

Can someone please guide me on the exact steps I need to take? I have data on my Windows system so I can't afford to mess around. Would appreciate right guidance on this.

Thanking in anticipation :)

Partitioning screenshot 1 Partitioning screenshot 2