I think the grass is good, you don't have to clean the floor when u make a mess with soil spilling. Also the grass will stay short because you will spend the rest of you life in there
I would need a bigger door.....
What's the purpose of having a cage around your workspace?
I would just feel a little odd walking into a cage every time I wanted to see or work on my trees. Like I was stepping into a UFC match rather than my peaceful hobby. Maybe that's just me though. It sounds like you have a plan and have been bitten by the bug. Have fun!
I already have plans to add a shelf around it. One table is going to come out once that is done. More trees are definitely in the future....