Ok when initializing the extra drive should it be MBR or GPT
Most HDDs these days are MBR.
GPT I think is for HDDs
MBR stands for Master Boot Record, which gets its name from being the partition that contains the windows boot stuff, hence "Master Boot". HDDs that use MBR are very common and can work with disks up to 2 TB but cant go further.
GPT is designed to replace MBR with something moe modern.
Im not exactly sure how an HDD will work with an Xbox 360 HDD, but I would try MBR first