Fitler size recommendations

[CablingPro]

I bought a house with well water w/o any water treatment. It has high iron content and copper plumbing sustained a lot of corrosion.
I installed a sediment 10" cartridge and water softener.
I'm planning on installing 30 than 5 micron sediment fitters and want to use 20" housing. Which one do you recommend should be bigger or both?
Any other tips are appreciated.
Thank you.