You can download a program called cpuz https://www.cpuid.com/softwares/cpu-z.html it will tell you all the info about your computer click the memory tab it will tell you how much memory you have click the spd tab will tell you the type of memory. If you know someone that could install the memory you could order from Newegg I like G skill memory I use it in all my PC's.
Do not buy I just bought SanDisk Extreme Pro 128GB for 45 and was a fake amazon took it back it was sold from an outside vender speeds of 19 write and 18 read I own the real thing 86 read and 84 write and the price was only 10 more dollars.
I have a legit copy of PS Elements 15 and it will not update to acr 10 I believe, so I can not open my raw files from my canon 6d mark ii I will have to update to PS Elements 2018 and I think this is a ripoff. I have been buying PS Elements for the last 5 versions I would think they would update 15 to open the raw files.
I own a 6d mark ii and use a tamron 24-70 f2.8 di vc usd g2 and love it. I take indoor shots a lot and it is very good at low light. I also have the 50mm 1.8 lens and that is very nice also.
My niece had a pro at her wedding and asked me to take movies and I did, it made me very nervous but I am glad I did she did not like the photos from the pro and loved the movie I took.
I bought 2 battery's from aliexpress the battery's state they have Japan Sanyo Cells they make very good cells another one is Panasonic both made in Japan I was told that is what the stock battery's are made with and they cost me 27 with a charger. That is non OEM and work perfect in my Canon 6d mark iii.
I own the canon 6d mark II and the lens I use is the tamron sp 24-70mm f2.8 DI VC USD G2 and also the canon plastic fantastic 50mm f1.8 and I am very happy with the pictures it takes.
Graphics card's are insane right now because of bitcoin and using them for mining if you can wait a while something has to give and prices will drop then you can get a much better card for the same price.
I would do a fresh install if you clone all the old stuff you have comes with it what ever you installed and uninstalled there is nothing like a fresh install. The crucial is a good drive I have two of them with no issue I also have 3 Samsung with no issue but they cost more either way you will make that computer faster.
If I were you I would get the 500 gig ssd Crucial 500GB MX500 2.5 for 134.95 from amazon or B@H and do a clean install to the ssd and use your old drive for photos so format the old one do not use old one for operating system the whole point of an ssd is so the operating system is very fast.
I have 5 PC'S running in my house all networked with no issues. I think you will find all your mac stuff is running pc internal parts they used to make all there own cpu's and motherboards and video cards but the pc market is so big with lots of competition that they could not keep up so they now use nvidia Intel and so on they might make there own display not sure so on mac you are paying for the operating system. Please don't shoot the messenger.