Sounds like one of the benefits of a MBP, next to its ludicrous price and limited capabilities.
It would help to know resolution/codec of footage, but honestly I think I can answer without.
A) DSLR footage tends to be highly compressed which means processor and memory intensive to use.
B) Large amounts of footage will use large amount of memory.
C) Your system is not that high-powered. You will need to make some concessions to hardware.
I went back to one of my previous prjects with a lot less footage and it worked just fine so you are right. I don't have the money now to make upgrades but when I do, what would be the most crucial part to upgrade. Also, would you suggest (if I do another project this big) to only have a few scenes at a time in each project and then rendering them seperatly and joining them together into one file for now?
In general with computers, upgrading your RAM will give you the biggest bang for your buck. I would also look into getting an external hard drive solution - it's always best to leave 25% of your hard drive empty at minimum. Some people will insist on 50% capacity. The external is NOT for your footage or your cache. Use it to store some of the files using up so much space on your internal.
Working in segments will help keep the requirements down. You can always break down a larger movie into segments like acts and scenes. That's a good way of working in an NLE anyway - remember that a sequence can be embedded into another sequence. Just render out those sub-sequences when done, and that will greatly cut down on the amount of memory you will be using.