clarry: For disk setup, the first option is to mess with existing OS install. No way.
Well, it'll show that option when it detects an existing OS install. Many new users will want to dual boot on a single drive alongside an existing Windows install, so it makes sense to have a "quick and easy" option like that.
The second option is Erase Disk (which disk???) and comes with a red warning that it will delete all your shit in all operating systems. That is terrible! Don't delete everything! Don't delete all my operating systems!
Trusting adam's guide, I assumed the warning was written by some halfwit and went forward with it anyway. Indeed, it lets me pick a disk. Unfortunately the list doesn't include the disk I want to install on to, even though I can fuck with that disk just fine using fdisk and it shows up in dmesg. No go.
Yeah, I agree that it could do with being a little clearer. Just needs a small change, something like:
"Erase a disk and install Linux Mint
Warning: This will delete all your programs, documents, photos, music and any other files in all operating systems on the disk you select."
Strange for it not to show the drive you wanted to use though, I've not encountered any issues like that on any of the systems I've installed Mint on. It's quite likely that it's due to how your hardware is configured, something causing the installer to get confused (and/or maybe an EFI issue).
So the last option is to manually partition everything. Of course, the installer provides no aid and nothing like "just do a sane automatic allocation of space on this disk". So I have to come up with something. Decided I'd keep it simple, I create a small efi partition, and allocate the rest of the disk for a big root partition. Well, the partitioning tool decides to moan about alignment and tells me to delete the root partition and recreate it again at the same position so it will be automatically aligned. I do that, and it moans again, ad infinitum.
I'd guess the reason it doesn't have an auto-allocate option is because the automatic install possibilities are already covered by the other options (either "resize existing + install" or "wipe existing + install").
As for the alignment issue... did you try creating a new partition table on the drive first?