That’s a great deal with all those accessories. You can price all the other stuff new. None of these things degrade really, so functionality will be identical to new.
Only downside if you’re looking for one is the AM4 platform is done. Basically that’s a computer anyone would have recommended you buy 3 years ago new for what you’re budgeting, minus a few hundred for a mid range GPU. If the keyboard, mouse, and headphones are quality you’re getting a steal for someone in your position.
Yeah, upgrading the platform means Motherboard, RAM, and CPU. You’d be upgrading your GPU before then though. Don’t sweat it.