Please be aware that I am not using Veracrypt but I know its predecessor Truecrypt.
From what I've read I understand that it's possible I corrupted some of the key header data,
You are wrong and you could have simply found this out by reading the Truecrypt/Veracrypt manual. As this is outlined in a picture in there, no special computer knowledge is required!
Unfortunately you erased the first 5 GB of your hidden partition in case you did not protect your hidden partition using the appropriate checkbox in the mount options dialogue. Assuming this worst case the recovery work now consists in reading out the full unencrypted partly logically dammaged partition by means of addressing the new Truecrypt assigned drive letter in a windows system (you have successfully hidden the operating system you are using) as a source. The target could be a simple file for instance.
If you copied the content of the unencrypted drive into a file, some recovery programs might have difficulties because they might expect a drive image which usually starts with a partition table.
Therefore I would get a clean drive and partition it with just one partition without formating that partition.
In a next step I would copy that extracted file into the empty partition.
If this all sounds to difficult to you, consult a professional recovery service.
