Looking to upgrade existing i7 system, need advice

[AndyD]

I am looking for advice on what hardware to upgrade to make my system perform better (which was purchased as a bundle from Overclockers in 2018. I use the machine for gaming but also for standard windows programs etc.

Intel Core i7-8700 3.2GHz (Coffee Lake) Socket LGA1151 Processor - Retail
Gigabyte Z370P motherboard
Team Group Vulcan T-Force 16GB (2x8GB) DDR4 PC4-19200C14 2400MHz Dual Channel Kit - Grey (TLGD416G24
Zotac GeForce GTX 1060 Mini 6144MB GDDR5 PCI-Express Graphics Card
Raijintek Themis Black Heatpipe CPU Cooler PWM - 120mm
Phanteks Eclipse P400S Glass Midi Tower Case - Noise Dampened Black/Red
SATA solid state drive (not M.2) 500GB

My main focus is replacing the SATA drive. I see there are several read/write speeds available on M.2 SSDs, is it best to just go for the fastest I can?
What Graphics card upgrade should I consider? I am not looking to spend a fortune and be at the bleeding edge but something that is a good upgrade from a previous generation would be fine (to get the framerate up during gaming). Forza Horizon on Ultra settings has an average framerate of 12-20fps (so had to dial back the performance to find that perfect balance).

Any other suggestions for upgrades?

 

[AndyD]

Thanks for the advice everyone. I tested Forza again and was getting around 40 frames a second, with a resolution of 5120 x 1440 with Ultra settings. I have a budget up to £300, is this enough to boost performance with a new card?
I will get an M.2 SSD to upgrade the system anyway as my SSD HD is currently 500GB (and I need more space on the system drive)