The G-DEC 30 has approximately 2MB of storage available for MIDI files and will allow for storage of up to 64 songs(size permitting).  As far as the maximum size of a file goes, this is kind of a grey area because of the of the nature of file-systems(data is split between clusters and files are not necessarily continuous).  The Songloader will give you a warning if the file is over a certain size, but will only cause problems if the file system doesn't have enough room to fit the song. In that case the songloader will display a message and stop the file from loading. I don't know the exact size that will cause a warning but I think its somewhere between 100kB and 124kB.  Also keep in mind that while the space available is 2MB in reality it is less than that because the file-system has some overhead.