Just a note about "Samples" drives:
From a performance standpoint, you're better off with two 500GB SSDs than a single 1TB SSD.
You have two drives... each sustaining ~540MB/Sec vs. a single drive sustaining ~540MB/Sec.

Shoot, I've been just fine with a 160GB SSD for my OS/program drive.

I probably do things in an unorthodox way. I download most of my soft synths onto my C drive but I point the storage to another drive if the sizes are larger, hence the three drives I now have. One for large sample libraries. C drive for OS and synth programs and one for larger synth files  mixdowns/stems and loops. I also keep Cakewalk storage off of my C drive.
 
I mainly do this for one reason, If I loose my C drive and have it mirrored I don't need to go hunting for the files to those smaller footprint synth programs. Programs like Rapture are small in comparison to say, Omnisphere and I have no problem loading up my C drive with a handful of those. If the ONLY thing you want or need on the C drive is the OS you don't need much at all. I don't ever want one of those "Oh cr**!!" moments where I realize my C drive is low so I opt for a larger C drive, especially when after the first 250gb it only costs 30.00 for the second 250gb. 

The system drive in my current DAW is a 256GB SSD, which is more than adequate. My previous DAW (which is now the family computer) has a system drive of a mere 111GB, and there is still plenty of free space on it. I'm running Windows 7 though. I'm guessing that Windows 10 has more bloat.

Starise
250gb SSD-
https://www.newegg.com/Product/Product.aspx?Item=N82E16820250086
500gb SSD-
https://www.newegg.com/Product/Product.aspx?item=N82E16820250087
 
100% more storage for 1/3 more cost. The Samsungs are slightly more. WD and Samsung both get about the same ratings on Newegg.

 
My Crucial M4 SSD (Win10 and App drive) finally died last night; BIOS nor Windows can "see it." This has happened before after major Windows updates (somehow), and I could get it back by reflashing the BIOS.  Not this time, apparently.
 
I'm currently running Windows on an old 80GB HDD I had stored away. I will definitely be checking out these deals as well as some others. Are Samsung and Western Digital the way to go these days?

Price per GB in SSD SATA-III drives is cheapest in the 500-512GB range, so to answer the OP's question, I would go with 512GB at a minimum.
 
Furthermore, it appears the Samsung 860 EVO is one of the best, fastest SATA drives right now carrying a relatively low price.

I have been very satisfied with my Samsung 850 EVO, running daily for 2.5 years, and still at 100%.
 
The performance is great, even thought I am running a SATA-III (600MB/s) drive on a motherboard with only SATA-II (300 MB/s) ports.  I am getting 283 MB/s on a sequential read with a benchmark test.
 
That throughput still smokes a fast HDD, especially for sequential reads/writes.  The same test on my WD 1TB 7200 RPM drive only yields 152MB/s sequential.
 
The big eye opener between the two drives though, is the random access test.  Random reads with SSD can be 50x to over 200x faster than the HDD. 

FWIW, I just got back from Best Buy with a new 860 EVO 500GB.  $119...$2 more than Amazon. Helping keep the local businesses alive, lol!

I either have a delayed post or you might see a double post. Samsung seems to be the most popular around here. They work well and are very reliable. I wouldn't be afraid to try either one.
 
Congrats on the Samsung find 2:43AM.
 
I would be in trouble with a 250gb
 

 
 

So, I ended up going with two 2tb standard HHDs and, will probably add a 3rd one soon. I like plenty of storage.