Purchase priority next month

Your audio is good enough already that you are approaching the point of diminishing returns. There is room for improvement but nothing that would be comparable or as immediately useful as the security and freedom afforded by having a proper RAID setup.

I mean both in the long run but certainly more disk space for the moment. It's good you're making more money though!

Your audio setup is fine from a listener's pov. More storage is gonna help long and short term

As someone who works in IT, I would always go for the Data Redundancy. I'm not too sure what volume of data you work with but either a 4/6/8 drive NAS would do, 2 Drive NAS's are fairly limited in function. Synology are pretty decent running in RAID 5 or RAID 6 (Again, depends how much usable space you want). I would personally recommend RAID 6 over RAID 5 but you will get less usable space.

Ultimately do what makes you the most happy and don't regret it either way since they're both super useful and helpful.

I suppose it ultimately comes down to your long term goals and focus. I feel like the storage space helps benefit your youtube video quality more, but since you are starting to branch out into doing what is essentially an audio podcast (with a video component for YouTube viewers), the audio interface upgrades would go a long way for improving that content.

I vote for the HDD because at least with my audio setup, I can't tell anything is wrong with the sound, and the HDD seems like it would make more of a noticable difference.

From my perspective neither audio or video quality really seems to need improving much, so really just pick the one that makes your life easier

My opinion on the matter is drive space/data protection/redundancy is more important then improving already fairly good audio. If a hard drive or an array dies in the future its in your best interest to have a back up/archive available so you are not put out of work in an unfortunate circumstance. Obviously in the long run I assume you will end up upgrading both things I just personally think disk space/data protection/redundancy is a higher priority.

I recommend audio. The video quality is already fantastic, but I would hear the audio pop glitches from time to time. I also listen to your discussions while working so HQ video doesn't really make a difference to my consumption of your content.

your sound quality already on the top tier from lot of anime reaction YouTube. Sound like disk space investment would be more effective.

Terabytes of storage are infinitely cheaper and easier to acquire than good audio systems I think you should go for the audio Solution if you have available funds cause that's something you will need to save more for.

Never noticed audio problems while watching

There is not wrong or right answer here. A NAS is something everyone can benefit from. As a photographer, it's a dream to finally put together a raid array with redundancy to keep all my files safe. But I also have an absurdly overpowered mic setup for my needs. An SM7B, cloudlifter, interfacer set up. It's wonderful for recordings. Really, we benefit as your audience in either scenario.