You need to be deaf to not hear an HDD, and Helium one are generally very noisy.

Get a Synology NAS. A 4 bay if you have money, avoid the one with ARM CPU, get one with an Intel CPU.

You didn't say where you live and what budget you have. What solution do you want to plan, what HW etc. So I assume you live in Europe, amazon.de, going shuking, you would need 10x18TB drives for 292€ each, total 2920€. Then you can arrange it on RAID 5 and get 162TB, RAID 6 and get 144TB, or unRaid with double parity and get 144TB.

I just Google on amazon.de and do some basic math. It didn't take too much.

The DS1821 runs with Ryzen, so no transcoding capability at all. Anyway, most Intel solutions sell on those prebuilt NAS, don't have good performance, mostly enough for the basic Nas function, and mostly old stuff, without all codec support. You need an Intel CPU, one with integrated iGPU, capable of Quickl Sink.

If you need transcoding power, better go DIY. To give you a perspective, an i5 8400 can transcode around 4/5 4K video at the same time. As 1080p, we are over 20+ at the same time. That's the UHD730 power.