16GB of RAM from Apple and the 768GB Flash drive.
Get the standard 8GB and purchase any extra that you require from somewhere like Crucial.com
Your 1.5 TB external drive is only Storage, it is NOT memory.
If you have "massive amounts of music, videos, documents etc" then 768GB of Flash is not going to cut it anyway.
I think I would be trying to work out what's wrong with the previous Macbook. I really doubt that you have done "everything"
I have a 15 inch macbook pro. It's snow leopard, and i bought it 3 years ago during my freshman year in college. I had this thing enhanced and everything (it's an intel core i7, 2.66 ghz with 4gb memory, speed: 4.8gtc), but honestly right now it's worst than a PC. I tried everything, but it gets worse every day. I don't know if I did something to it without knowing, but I cannot stand it anymore, and if I have to optimize my discs (or any kind of thing like that!!) for one more time I'm gonna go crazy. So I'm buying a new macbook pro with retina display (15 inch) and the end price is $3749.00 with:
2.7GHz Quad-core Intel Core i7, Turbo Boost up to 3.7GHz
16GB 1600MHz DDR3L SDRAM
768GB Flash Storage
I added pretty much everything i wanted, but that's a lot of money. could i have my "dream machine" without the 768gb flash or the 16 gb memory? I have a 1,5 TB external drive, so could that compensate for the memory? or should I just get the whole thing? by the way, I should note that I have massive amounts of music, videos, documents etc and I have thousands of software that take up a lot of space and require the highest performance possible.