I often add brown materials to my soils to improve tilth, but I always shred them first. They will break down over time, but much more slowly in cool soils and larger sizes. Short of raking the beds out, you might try compost tea or a high N seaweed or fish-based fertilizer to introduce some "green kick-starter" into the soil. Black plastic may create conditions that are actually too hot for the biota to start the decomposition process. Clear plasic on low hoops might give better results - either way, adequate moisture is critical for decomposing brown materials. The other alternative is to add soil or compost on top of the beds and plant into that. The decomposition of primarily brown materials should do little harm to germination or growth of seedlings, and unless the leaves are very matted, they should find easy passage through the soil and organic matter.

Are you making a raised bed so there would be soil on top of the cardboard? If so, and you're adding soil, it really shouldn't matter how wet the underlying soil is. If not and you're tilling up the existing soil to amend, it's best not to do that when wet if it's a clay soil. Other than that it shouldn't matter.

I'm with PeterK2. You need to add more holes. Ideally, there will be a lot of holes on the bottom. You can place the bin inside another bin or on the lid it came with to collect water that comes out. It's called leachate. If you're working it right, there won't be much water in the lid. Here's why. Though worms sometimes eat the food directly, they mostly eat the bacteria that eat the food. The more oxygen you have going through the system, the more bacteria you'll have, the faster the growth of the worms will be. Hot air rises, so air will be sucked in to the holes on the bottom and pulled through the mass of VC. This is the main idea behind flow through bins and stacking bins. One source recommends 50 holes of 3/4" size. I didn't count when I added holes, but I added a lot. I started with smaller holes and they got blocked with muddy VC that dried out and it ruined the whole thing. If you don't want holes on the bottom, you can put them about an inch above the bottom of the bin all the way around. You can put screening in to cover the holes, but it's not necessary. Very little VC falls through, even with 1" diameter holes. The worms can go through window screen if they want, so the screening won't stop the worms. The only time the worms will leave is if something's wrong with the environment. So if you have worms leaving, you have a problem. For me, the problem is usually overheating from adding too much food. Before I added the holes, the most common problem was pockets of anaerobic (REALLY stinky) VC. That hasn't happened since I added holes to the bottom. As to your second question, the few times I've mixed the food in with the older VC, things have heated up badly and I've killed worms. I keep a couple of inches of moist, shredded newspaper on top and lift that up to add food to the top of the working area. Every couple of weeks, I add the food to the top of the newspaper and add more newspaper on top of that. This minimizes flying bugs. According to those who do this on a large scale and more scientifically, you're supposed to have 20x more bedding than food. I don't go that far, but basically, you can't have too much bedding.

I wouldn't say when coming home since my SC do not have extended visits with their mom. But I think it is stress related with my 8 yr SD though ... if her and mom had a "tough day" she has accidents she goes off into a daydream of sorts ... she sleepwalks and urinates in the hallway... she even vomits while she is sleeping (she stresses herself out over what I call minor but to her major incidents so much she makes herself sick). And their mom used to put all her problems on their shoulders. They couldn't carry the load and would just crumble. She made fun of a kid at school and told the other girls to make fun of him too. Came home and cried and vomited damn near had a breakdown over making fun of the boy. For two days straight nothing eased her mind or body. She would urinate on herself ... then go to take a shower and vomit on herself in the shower. This does not happen often but atleast every couple of months she is "stressed out" about something. If it goes away in a couple days after return probably just the stress of being back and forth not a major big deal. Next time they visit BM put the rubber sheets on the bed before they get back. :-)