Does it indeed come with only Samsung bloat pre-installed?
Yes it does. Things like Samsung Health, Samsung browser (Which I prefer over Chrome), KNOX, Hancon Office Editor, Samsung Print, Samsung+, and what not.
But to be honest with you it's very minute IMO. I think it's very lean.
Can any of that be disabled/uninstalled?
Some of them can; Hancon Office, Samsung Print, Samsung+, Dictionary, and others can.
Is all you had to do was insert the sim card from your old phone and you were good to go with your carrier?
Yep, I came from an iPhone 6S Plus, sold it on Swappa to fund my S7E. I didn't do anything other than throw in the T-MOBILE SIM. I tested it on AT&T for like 5 minutes. All was fine. Wi-Fi calling works with T-MOBILE.
Have you received any OTA security updates and/or Android updates since you got it?
Unfortunately no, I'm still rocking May 2016 and the T-MOBILE S7E is on July. The rumor is there might not be updates for the unlocked version in the US. There was some controversy on it when Samsung tweeted no updates for this model. As the article stated that's likely false and just someone saying nonsense. But proof is in the pudding, I'm on May.
Any idea when the unlocked S7E became available after the S7E was initially launched?
Think it came out last month if I'm not mistaken. The carrier version came out in March? So like 4 months.