Complemental components to upgrade PC?

We have an old PC at home which I recently dusted off and installed Win 7 to (was XP) (W7 was the newest OS the PC’s RAM would be able to handle).
However, I’m thinking of “polishing a turd” and upgrade it.
From other PC builds I’ve done through the years, I have a few extra components I think I could use;
MB: Asrock X99M EXTREME4, and
PSU: 760W.
The old PC currently has HDD: Seagate Barracuda 250GB,
… and of course MB, RAM, CPU, SSD and GPU (integrated to the MB).
These latter components would have to be changed, of course. DDR4 RAM, GPU, CPU of LGA2011-3 socket, an SSD, and a CPU fan.

So, my questions: Any tips or advice for what components to buy? Which CPU, GPU, how much RAM, etc? And also, is the current HDD enough or would I need to buy a new one?
I’m not aiming for an extremely high end PC (I have another one with 980Ti etc for that), only a well-performing, okay-ish one that can handle modern games at low or medium settings and so on.

The X99 platform is pretty much the antithesis of “okay-ish”, the minimum performance of X99 is “a lot”. If it’s solely for the purpose of gaming at low/medium I think you’d be better off selling your X99 motherboard and swapping to something like an Athlon X4 or equivalent, parts are significantly cheaper outside of X99.

Anyways, do you have a budget? Anything else you’re going to use it for other than gaming?

Rough PCPartPicker list:

CPU: Intel Xeon E5-1620 V4 3.5GHz Quad-Core Processor
Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler
Memory: G.Skill Ripjaws 4 16GB (2 x 8GB)
Storage: Intel 600p Series 256GB
Video Card: MSI Radeon RX 480 8GB ARMOR 8G OC Video Card

I don’t understand your question…

You have an old computer, you want to upgrade it but you’re going to change everything from what I read.

@Deathspell Well, yes and no. Essentially, I guess you could say I have a motherboard I need the rest of the components to, and I already have a PSU, case and HDD, so.

@w.meri Yeah, I was guessing the parts for the X99 would be quite expensive. True, it isn’t a mediocre motherboard, it was just, I already have that, so I felt like I could just as well buy parts matching it when i wanted to upgrade a computer anyways.
I’ve been thinking about selling the X99, however I’m not sure how the second-hand market is for PC parts; if I’ll be able to get any significant money from it (and where to well it, like, eBay?).

I don’t really have a budget tbh, no.
Not going to use it for much else than gaming; my family will probably use it for internet browsing and like, MS Office programs (it’s at my parent’s, and I wanted to have a PC there that can run games), but no heavy things like video editing or such.

Check on ali express they might sell a lga 2011 cpu for dirt cheap

Kaby Lake will have an unlocked I3.
GPU? Shop around for sales and something will jump out, something interesting:)

The case. Now is the time to try something wild:)

So, you’re just going to re-use the case and PSU?

I would put a new SSD, max out the RAM with some used DIMMs from Ebay, and get a new mid-grade GPU like a 6GB GTX 1060.

I’d re-use the CPU and board in it since you want to use Windows 7 anyway. You won’t be running software to utilize new instruction sets.

Clean off the old paste and apply new paste like Arctic Silver Ceramique or the Noctua NT-H1.

I would also probably re-flow all of the solders in the board and RAM using a heat gun, but that’s just me.
You could also re-oil and re-seal all of the fan bearings, or just replace the fans.