Should I order from Apple or just get one off Amazon?
All things being the same bit of an advantage ordering from Apple. Amazon support isn't bad, but Apple's is much better if you have a problem since they are experts on the product.
What about the lightning port is bad?
As mentioned the latest iPad Pros support thunderbolt speeds.
Oh damn so what should I get as far as gigabytes at a minimum?
Depends on how much space your applications and data take. Since memory is not upgradeable if the option is available I'd overbuy if you can.
Can videos also be stored on an external storage? Pictures videos and what other things?
As above you could store anything you want on external storage. Take into consideration:
Only the later Pro modes have thunderbolt transfer speeds
Make sure that the apps you use support external storage or you might have to do some convolutions like copying data from external to internal storage. [Confession - don't use an external drive with my Pro so my experience is limited]
External drive support isn't as good as it should be. No eject option, reports of data loss on SSDs when removing them so you have to be cautious.