I'm no exercise expert at all, so don't take my word for any of this:
So for one thing, are you saying that you do 30 mins on the tread and then 30 mins on the elliptical? If so I think that's doing a bit to much. I think doing 30 mins -45 mins max is good enough cardio for one day. so if you want to work out both i say split up the time. I usually do 20 on the treadmill and 15 on the elliptical, but then again i'm new to the exercise scene so if that's too easy maybe you can do 25/20 you know?
And I understand the whole no outdoors thing, I use the treadmill as well. And doing intervals isn't bad at all. Its actually good for you if you're starting off with running. I learned that recently (I'm trying to start running

)
Oh and with the holding on to the bars of a treadmill, that's not good. If you do it for literally a second to just take your heart rate than that's perfectly fine. But you won't be working anything out because when you actually walk your not holding on to anything, so in a way you're not making any progress. When you walk to kitchen and back, you're burning more calories than you are when you're walking on the tread for 5 mins while holding on the bars. And that may be why your arms hurt.