I have a 2504S, which is very similar to your 2509S. I'll answer the easiest question first. No, you definitely cannot lower your murphy bed with the slide in.
Look at the floorplans below. You can clearly see that the slide portion (Ward and the grey carpeted lip noted in the 2509S) in each case is identical and overlaps with the edge of the bed. No-go. Bed stays up until the slide goes out.
As for the access, it's one of the reasons we liked the 2504S. If you look at the shape of the countertop, the 04S doesn't extend out toward the slideout wall. The 09S has a discrete L-bend that reaches toward the slideout wall. I can easily squeeze by the counter in the 04S. My average 5'11" 180 lb frame couldn't do this on the 09S. I had to saddle across the dinette cushions. But, with reasonable effort, I could get back to the bunks/bathroom of the 09S ... it just wasn't a straight walk-through like with the 04S.