I am looking at encrypting documents, media, etc with BlowFish 448 and some of the files exceed in 20GB in size. Is there a risk of using BlowFish over AES 256? If so what are they?
There is no limit to the size of files a cryptographic algorithm can actually handle - however, depending on the use case there is a theoretical risk inherent with larger data sizes.
Firstly, Blowfish is not known to be broken at the current time of writing.
Secondly, it is a block cipher and as such is just a primitive. All block ciphers are used in conjunction with a mode of operation such as CBC. Due to the birthday paradox, after 2^32 blocks (for 64-bit block size ciphers) collisions become likely. That basically means that after (64*2^32)/((1024)^3) gigabytes, you have a problem. Luckily for you, that works out at about a 256 gigabytes, so at the moment this is just a theoretical issue.
Clearly, if we were using 128-bit blocks, we'd use the formula (128*2^64)/((1024)^3), which gives us an insane (something like 4 trillion) gigabytes to work with.
Bottom line: this should be more than fine for a 20GB file.