Upgrading My Desktop Computer: Choosing Cpu, Mb And Other Components

Having had so many problems with my desktop computer in the past year, I have decided to upgrade. I've decided to replace the motherboard, CPU and RAM and buy an SSD for the OS and programmes.

Currently, I have the following:
• Motherboard: MSI H61M-P21(B3)
• Processor: Intel Core i5-2400 Quad-Core Processor 3.1 GHz
• 2x 8GB RAM
• Graphics Card: NVIDIA GeForce GTX 260
• AVerMedia A323 MiniCard Hybrid ATSC (Used very occasionally)
• 3x internal 1TB HDDs
• DVD Drive
• ATX-P4 600W power supply

The computer is used for regular home activities as well as photo and video editing (Photoshop and Premiere Pro). I don’t play games. All my videos, photos and music is stored on this computer. Win10 OS

The following was suggested:
CPU: Intel 8th Gen Core i5 8400
RAM: 16GB DDR4
MB: Gigabyte B360 DDR4

Questions:
1. My biggest uncertainty is regarding the CPU. The i5 8400 is selling in my country for USD288, while the newer i5 9600 is selling for USD414. As I use of the computer for video editing, should I rather spend the extra money?
2. Please comment on the choice of a MB?
3. Would it still be necessary to use the graphics card with the new CPU?
4. Would I be able to use the new SSD as well as the 3 internal HDDs?

Any other comments?