With most plants it is best to up pot gradually in size but with BB and imho they benefit from the larger container right off the bat so I would have no qualms putting them straight in to the 15's.

Your mix is too water retentive. If you watered them in good then you need to let them dry. Dump the water trays and don't water until the soil is dry on top. You'll have a hard time curing root rot with that mix. Take the nepenthes inside and stick the pot in another pot with dry sphagnum in it. This will help dry the soil. Maybe use some LFS to sponge some of the water from the top soil also. Do not water any of them until the top of the soil is dry. Only use a half cup or less in each plant after the dry out on top. I know I'm sounding like a broken record but you can make this soil work if you are careful about watering. You dont want to repot them again until they show some active growth which could be spring for the temperates and could be 2-3 months or even longer for the Nepenthes depending on the severity of the rot. You might also poke or drill some hole in the side of the pot near the bottom. This will allow some air to the roots.

First question for you would be whether you've totally fixed your soil and made it well-draining as has been recommended. High in pumice, perlite, turface, chicken grit, whatever you found available to you. If not, that needs to be the priority, as watering anything in poor soil could give you rot. If your soil is correct, then you can begin watering (not misting) rooted cuttings once roots have developed, and begin the typical watering schedule of watering thoroughly when dry. Same goes for rooted leaves. And when I mention a cutting, I mean a portion of a plant (with some stem, for instance) that has been cut away from a grown plant to root separately. A rooted leaf is a rooted leaf in my book, not a cutting. The roots on newly rooted leaves are very delicate, and to avoid accidentally knocking them off the leaf, I might recommend dropping a pinch of the soil on top of the roots rather than trying to stick the rooted leaf end down into the soil. No need to transfer the leaves to another pot once they've rooted unless you've yet to make a pot with a proper soil mix. A bunch of leaves set up around the edges of a pot, basically right on top of one another, can root and begin growing new plants and be just fine for a couple months or so. It'll be a little while before the individual new plants or their root systems become large enough that they'll really be interfering with one another. They don't need to immediately be given a lot of room. As for misting unrooted cuttings, you can do that every few days and it's a good thing to promote roots. I don't mist a lot of my unrooted leaves, but some of us do. I think we might shy away from recommending misting because many new growers are really inclined to go overboard with it, just as they're inclined to go overboard with watering succulents in general. And misting is not critical to rooting, say, Echeveria and Graptoveria leaves, which root perfectly in dry soil and are easy to cause to rot-- for me their leaves root like weeds and I just don't find it necessary to mist them. I personally may periodically mist unrooted Kalanchoe leaves or a leaf that isn't as easy to root as an Echeveria leaf, and it can be very beneficial in encouraging roots to form. Unrooted cuttings I oftentimes will lightly mist every few days to encourage roots--two to three times per week, I'd say--and the same goes if I've decided to light mist an unrooted leaf. I have one leaf cutting that had rooted. But I have actually forgotten about this particular cutting until I saw it again yesterday while I was cleaning. Haha, and that's your first success, eh? See, that shows ya, there's a plus to being neglectful. Don't worry too much, don't fuss over things. If you stick a leaf in soil and walk away and forget, that's the one that's bound to reward you. :) This post was edited by teatree on Sun, Jul 21, 13 at 17:31

Not sure how well plastic will drain (it won't, but it may eventually run through cracks in the bed bottoms). I know it's an expense, but if your grass will grow through paper (and cardboard), try landscape fabric. That's what I use. As for the dirt mix, fresh manure needs to be composted to insure that it doesn't burn plants. Also, one source of compost is 4 less than Mel recommends, but use what you've got. Though you may want to try some lasagna techniques to compost in some free coffee grounds from Starbucks (get as much as you can, I'd say two bags per layer of compost plus some shredded newspaper would help. Maybe some grass clippings thrown in for good measure. Sure it's work, but make it gardening fun and your plants will love it. Or better yet, mix it all in your new tumbler and let it do it's thing over a few weeks and then use it in your beds. Peat moss and vermiculate are optional, but recommended. Getting some of both could work, or one or the other. Folks here have had success with all combinations. Good luck! Here is a link that might be useful: Sinfonian's garden adventure!