Spec my rebuild?

I am going to hold my hands up here, I am so far out of the game in terms of hardware builds, i'm not convinced i could spec a working machine up from scratch anymore. The learning curve feels enormous, especially for an unraid server build and the quirks that come along with it.

There are some enormously helpful people in this community, so if possible, i'd like to drop a few thoughts in here, and work them into a full new build with their help.

My existing position is that I've got a server running unraid, that I think is coming up to 10 years old now, running very old hardware. but obviously, in that time unraid has been a delight.

My use case is relatively straightforward - at the moment the server is mostly a media server that runs Plex and a few other related dockers (i.e. sabnzb & deluge). It's mostly used in the house, but I have a couple of external users on Plex. I am interested in a few other dockers, when I upgrade, immich, homeassistant and possibly some home secuirity stuff, but nothing that requires too much heavy lifting, but i would like to build it and forget to a degree, i don't want to keep upgrading.

I've got around 9 drives at present, ranging from 20tb, to 4tb. (excluding cache)

I would like the build to be rackmount as i have a cab in my garage, but it's not a deep one. I do have a case which i'd like to use, it's not identical to this, but more or less the same: https://www.theserver.group/products/logic-case-lc-4480-8b-wh-4u-rackmount-storage-chassis-8x-3-5-sata-hot-swap-480mm-short-depth

My initial thoughts are i'd need an additional rackmount disk case (I don't know the correct term for these devices!) to allow for my current setup but also compensate for expansion in the future.

Budget wise, realistically it would be around £1k - but obviously this doesn't include a case or HDDs. If it's really necessary, i could go about 50% more i.e. £1500, but I don't want to spend excessively unnecesarily.