You can connect the Blu-ray no problem, the issue is if you can play back the content.
As above first option is to run a virtual or boot camp windows install (again … virtual would be my recommendation). Higher chance of an available driver, and more software options.
Option two is IF (and its a big if) the MAC OS recognises / supports the drive then you will need to invest in the appropriate software to read and decode the DVD / Blu-ray. I was supplied with “vlc media player” which while buggy was useable for the external super drive. No promises if it works with Blu-rays (as given previously, its an unsupported format by Apple).
External Hard drives, no problem but you will no doubt need to reformat them for read / write if they are NTFS. Fat32 will allow cross platform read and write, while Journaled will be Mac compatible. You can also boot from USB on an apple so good idea to partition and clone a hard drive copy, or use as a Time machine backup.
Regards memory, if you click on the Apple logo top left of the screen, select About this Mac, scroll down to memory it will tell you what it is presently running. Pre unibodies most ran DDR2, then post uni went to DDR3. They are not interchangeable. While Macs are more sensitive to clock and latency speeds, as a general rule if your existing memory is equal or higher in clock speed, it MAY work.
The crucial website also has a memory finder based on Machine model which you could use.
Re the OS vs Windows flame wars, i prefer the Mac hardware (im a sucker for bling) and the reduced system threat level, Given that I need to integrate into an existing windows server system then a virtual Windows system keeps things very simple. Also as per the OP I came from a dead Win. system so had a high level of investment in Win. software. Apple at least gives me the flexibility to continue to run this.
Nothings perfect … thats why we modify 🙂