Other than the mold in the office next door, sounds like a lovely place to work, with only a 15 minute walk. Nice! Working from home is not for everybody anyway, even when it is an option. Although, I thought I would hate it (I was practically forced to go home), I ended up liking it, because of course I get to spend more time with my BFFs (the birds lol).
The sleep cage could just go on top of the regular cage, provided it has a flat top. The idea is to keep him out of his daytime cage until right before you leave...keep it locked until then. You seem to leave early enough, that I would not even let him in there to eat until the second before you walk out the door. In the morning you would open up his sleep cage, of course there will be water in there, and you can put some snacks in there in the morning. And then spend time time with him away from the cages, bring him in the shower with you using a shower perch, have him hang out with you in the kitchen while you are preparing his food, do some physical activities with him.
When it is time for you to leave, let him sit and watch you set up his daytime cage with new toys and activities, and the food. The idea is to get him excited about his day, and build up the anticipation. So that he doesn't see you leaving as a bad thing, he'll see it as the time to get into the fun cage with all the food and toys and activities. Also, you will need to wake up early enough to spend all this time with him, which means you may need to change his natural schedule a bit. He will have to go to bed earlier, so that he can wake up earlier. My cockatiel is ready for attention the second I open the cage, even if it is dark out. My Eclectus however, gives me the grumpy bird back for a good 30 minutes or more, before he is ready to even come out. And even then he ignores me for like another 15 minutes. If your birdy ends up being like my Eclectus, then I would suggest going out there early, maybe about 30 minutes, flick a couple lights on, say good morning and put on the TV low volume. Go back to bed for 30 more minutes, or whatever you want to do on your own. If not, what could happen is right when they're starting to wake up and really gearing up to get attention from you, it's going to be time for you to leave, which could leave them mad and frustrated with you.
Sorry for the book! I just had experience with this with my birds, and guilt drove me to find the best solutions. And all of these things worked really well for us.
