Limits of upgrading components?

RAM and a SSD swap are a must at this point, but these laptops will run nowhere the speed or resolution of a modern laptop. With the age and problems with some of these laptops id stop at those two upgrades.

This being said, this laptop will still run a relatively new macOS version and will be usable for more basic tasks.

MacBook Pro laptops don’t offer replaceable CPU’s & GPU’s (most newer laptop systems don’t either). You could replace the full logic board but are often limited to what the series used, so in your case these are the three possible choices 2012 15” MacBook Pro’s - MacBookPro9,1 So its best to get the one you want (can afford and/or find) for a working system Vs trying to piecemeal a system together.

As far a RAM the max this series can support is 16GB (two 8 GB SO-DIMM’s) For drives you can put in any 2.5” HDD or SSD. that fits within the cases limit of 12.5 mm in height. uAs an example a Samsung 870 EVO comes in 250GB, 500GB, 1TB, 2TB & 4TB sizes all will fit and work without any issues.

Now the down side… The highest macOS this system will run is Catalina officially. I really don’t recommend using APFS on SATA based drives (system drive) so the highest I would go with Sierra which is the last macOS that uses HFS+ file system.

The HD drive bay SATA cable tends to have issues if you have an older version. As such I do recommend upgrading it to the current version which iFixit sells and don’t fold it as many people damage the cable you want a nice radius of a curve where the cable needs to bend around.

So your usage is limited to Intel based app’s as Apple is moving to their own M Series SoC’s (CPU/GPU and other stuff in a single chip/carrier) and app developers are quickly moving to support the new M Series SoC’s. That adds a wrinkle here as most of these newer apps will require Big Sur and newer to work properly.

Hackintosh route is also at a dead end soon as well, as soon as Apple stops supporting Intel.

Now some good news! This will likely take two to three years to rollout so you still have a sizable use window. For reference I’m banging on a 2012 15” MacBook Pro right now.

This system is a good general purpose system. It is not as powerful as the new M1 Pro and Max SoC systems so if you are doing heavy game play or professional work it won’t be a good choice. If you are writing, basic presentation, web browsing and watching YouTube videos then this will be just fine!

Just like buying a car we all don’t need a Porsche, when a Jeep is more than fine.