Three Questions

[SlitherinSisters]

First question: should i block out the back and sides of my snake's tank?? I see some who do and some who don't...just want to do what's best for Mycroft

You don't have to. It's something people do if the snake is not eating, helps them feel more secure.

Second: Mycroft makes a whistling noise when be exhales rapidly...normal or aberrant??

Could be from shedding. Just keep an eye out for bubbles/mucus coming out of his mouth. That would be RI.

Third: Does he NEED to have 2 hides?? I have one that is a half log (my original one I got for him in my time of ignorance) and a second one that is a dome-shaped one. He seems to spend all his time in his dome one, and with both hides and his water dish he doesn't seem to have a lot of room to move around in the 20 gallon tank he's in.

No, as long as your temps are correct. Anything older than a hatchling in my house does not get a hide. They are all in a rack system though so that helps them feel more secure. I recommend always using hides in tanks/large cages. He's using the dome hide because he feels more secure since it only has one entrance and it's much more enclosed. Log hides are too open, most bps don't care for them. If you want to have two hides they need to be identical because the snake will chose the one it feels more secure in regardless of their temp needs.