Imac upgrade for 4k editing

Hi.

Iam looking to upgrade my imac so it can edit 4k video without any problems. This is my current imac specification.

Imac 27" 3.2QC/M380/CTO

3.2GHz QC i5, TB upto 3.6GHz

Memory 16GB 1867MHz DDR3L (2 x 8GB)

Hard Drive 1TB Fusion Drive

Graphic AMD Rawdon R9 M380 w/2GB

Iam proposing to up the memory to 32GB and add a Blackmagic external eGPU Radeon Pro 580 8GB and install Final Cut Pro.

Will this work well or do I need a new imac?

Thanks