Investing in an FX platform new is different to getting a CPU upgrade which is better than an i3 and keeping 20GB of RAM from becoming obsolete using a high end board you already have.
The 9590 is half way between an i3 and i5 with solid performance for the money.
Buying RAM on top of an i5 and B250 board wouldn't leave much room for a good GPU upgrade, limiting you to the 1060 3GB.