Any recommendations for a where I can get upgrades done?

Any recommendations for a where I can get upgrades done?

I want more than the ‘allowable’ upgrades on my iMac 21.5 inch 4k (2019 year). I see through this site alot of people have made the following upgrades and they seem to be the best of the best. i9 9900k CPU, 1 TB SSD, 8TB HDD and 64gb RAM. I am no where near confident in doing these upgrades myself but was wondering does anyone know a place or someone who would do these upgrades that aren’t your most normal ones to do.