Storage options for upgrade

###Build Help/Ready:

Have you read the sidebar and rules? (Please do)

Yes.

What is your intended use for this build? The more details the better.

Primarily gaming, some streaming and lit office stuff.

If gaming, what kind of performance are you looking for? (Screen resolution, framerate, game settings)

I'm looking to get more of my steam library onto my storage at one time but keep it SSD based.

What is your budget (ballpark is okay)?

£200-250, £300 at a push.

In what country are you purchasing your parts?

UK.

Post a draft of your potential build here (specific parts please). Consider formatting your parts list. Don't ask to be spoonfed a build (read the rules!).

Currently running a crucial Bx model SSD of 500gb, either the 100 or 200, can't remember. It's serving me well but would like to upgrade to larger storage solutions to fit more of my games on it at any one time without redownloading since steams download rates have been crapping out on me lately.

Motherboard is z170 pro gaming, has lots of sata connections and an m.2 too as far as I can see.

Wondering what you would recommend? I've been considering the following options:

1. get another 500gb Sata ssd. The perfectionist in me wonders if getting another crucial model to make two identical ones would be better? Or just get what I can pick up on a good deal? More to the point it's been years since I ran two hard drives at once so I'm not aware of any finicky bits, advice would be great.

2. get a 1tb Sata SSD, probably a Samsung 850 or something, and just suck the price up and deal with it. Easier for my peace of mind.

3. go crazy get a small m.2 drive for OS and key games and put everything else onto the existing drive.

4. go absolutely bonkers, throw out the budget and get a 500gb or even 1tb m.2 drive like the Samsung 960 provided it was compatible with my mobo. Option only three if it would be worth it? I'm guessing not but I'm not an expert.

Provide any additional details you wish below.

Thanks for any help you can give me. Sorry about the length.