mainly for the integrated graphics to use jellyfin’s hardware transcoding. Is the UHD 730 enough for that?)

My 4th gen Intel i5 can do that

No idea what to get for MB

You get the cheapest thing available with your socket that has at least 4 sata slots for migration

Server quality storage is extremely expensive, not sure if its worth buying.

Just get 2 WD blues

For case I saw some suggestion for cases with a ton of hotswappable drive bays

Or, you know, if you are making a whole post crying about your financial situation, maybe you can just move your ass and manually swap the HDDs.

PSU I want to get any gold PSU with low wattage from a reputable brand

If you want something energy efficient, why in gods name do you want to buy a desktop CPU?

16gb of any decent ram I suppose?

If you want to be fancy I guess, but my 25€ half dead optiplex that dosent even pass its own self test is currently running on 8 gigs of DDR 3 storage I got out of dumpsterdiving in a junkyard right before they threataned to call the police on me, and I live in goddamn Germany, so maybe make up your mind if you want to be crying about being poor or actively going out of your way to buy fancy Server Equipment I can only dream about in my setup.