Recently, CAS has been crashing for me and I think it's to do with loading difficulties. I suspect that it is crashing because of CC. On my cleanly installed version of the sims 2 Ultimate Collection, when I wasn't using much CC, the game ran fine in CAS. Only recently after downloading the CAS wide screen fix with more columns (seen here: https://modthesims.info/showthread.php?t=623172), it seems whenever the game tries to load clothes, whether the clothing is CC or not, the game may randomly crash. The game also crashed when I was done creating a family (which had me worried as I thought the family would have corrupted data). Outside of CAS, everything seems to be working fine, playing the game as normal is fine but in CAS, the game keeps crashing. When it does crash I get a "The Application has crashed. The application will now terminate". Could it be crashing because the game needs more RAM (I haven't applied the 4 GB Ram fix to the sims 2 yet) or is it CC that is creating the issue?

Quite likely a RAM issue. If you have 6+ GB of RAM, the 4GB fix is absolutely recommended.

Once you have installed it, and if the game is still crashing, then you can test to see if it's CC. There's not much point in testing CC if you're getting random RAM crashes, because removing CC is probably going to calm those down anyway.

I made the game run on more than 2 GB of ram and so far it hasn't crashed yet so looks good. The way I did this was through the CFF Explorer method. However, does it only make the sims 2 run on 4 GB of ram or is it possible to make the sims 2 run on more?

4 GB is the limit for TS2.

If I've understood it correctly I think the 4GB fix is pretty much the same as the CFF method, but a somewhat safer and easier method for those who aren't comfy editing the files the hard(er) way - especially when the 4GB fix involves just a couple clicks and is relatively beginner-friendly.

What is the harder way and what does it do?

Not sure if I misunderstood you the first time around, but there are a few variants of doing this edit - the hard(est) way (no programs needed) for those who know what they're doing and can do it manually without having to download a program to do it, then there's a program that lets you edit these files much easier (but still a slightly "harder" method, if not particularly hard technically speaking - I think that's the CFF Explorer from NT Core you used), and the really easy way (4GB fix) also from NT core (I think?) that pretty much does everything for you.

If you used CFF Explorer, edited the appropriate exe file (for UC users, that is Sims2EP9.exe), checked the box that says App can handle >2gb address space, and saved the exe file after doing that, then you have applied the "4GB fix". (See attached photo.)