1 file might be for GCkey, I have just sent them a webform there are multiple files allow but under the limit of 3.5 MB.For GCKey account, as far as I remember, only 1 file is allowed.
There is a size limit for the attachment too but I forgot whether it's 2MB/3MB/5MB.
When you are planning to land.? and where you will land.?
Thank you God bless you.