For the Intel® SSD 750 Series (400GB, 2.5in PCIe 3.0, 20nm, MLC) you will need to have the NVMe* drivers installed so Windows* can recognized it. You can find it here: Intel® Solid-State Drive Data Center Family for PCIe Drivers - Notice that the drivers are offered in both architectures, 32 and 64 bit, be sure to choose the one that matches that of your O.S. and also, make sure to read the installation Guide and the Release Notes as needed to guarantee proper installation.
Using our Intel® Solid-State Drive Toolbox you will be able to run Secure Erase on the drive as you see needed but you can also use the option offered by Windows* by accessing Device Manager. *Before procedure such as this one, it is recommended that you have all your files backed up in order not to lose important data.
Regarding the partitions, there is not an specific recommendation. You can choose the size you think it is suitable for your files, just remember that you need to leave enough space for the O.S and its updates on the partition designated for it.
We hope this information helped you.
You didn't really answer the main question. What size allocation unit should I use when formatting the drive?
The basic page size of the SSD is 4KB. You can use any multiple such as 8KB or 16KB that should work just fine. For additional information only you can check on this third-party website: What Should I Set the Allocation Unit Size to When Formatting?
*NOTE: This link is being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.