>1. How many diapers do I need?
depends on how often you want to do laundry. i've heard of infants that only poop once a week. if that were the case, you could get 12 fuzzibunz or happy heinys and do laundry every other day probably. if you have a poopmachine like me, you'd be doing it daily. well he's slowed down to 1-2 times a day now, but man oh man did he poop alot the first few months.
now we've got 12 motherease one-size diapers with 6 snap-in stay-dry liners, 7 happy heinys, 3 harleez diapeez pocket diaps, 3 kissaluvs fitted, 3 motherease sandys fitted, a bummis super whisper wrap, 2 motherease airflow covers, a sugarbums fleece cover, 2 prowrap AIOs, and a freshies AIO. i do laundry about every third day though i have enough diapers to go longer than that - but i wouldn't want to let them sit for more than that! (and just so no one thinks i went totally crazy on diaper buying, i inherited all the motherease gear from my sister-in-law for free!)
>2. How many diaper covers?
you *could* get by with 2 - one to use when the other one is wet/poopy, but i'd say you'd want at least 3, if not 4 or 5.
>3. Do I use something different at night?
I save the happy heinys for DH to use - he doesn't like snaps or covers. they're the closest to a disposable. i double up on the inserts (microterry towels and hemp fleece that i ordered online cut into 12x15 rectangles that i fold into four layers) at night and can go about 10 hours before he starts to leak a little. he's a pretty heavy wetter these days.
>4. What sort of detergent should I wash the diapers in?
depends on the diapers. if you have fuzzibunz or happy heinys, you should NOT use a free&clear detergent because it will cause the fleece to repel instead of wicking through to the inserts. something like tide or the cheapo costco brand works fine. if you don't have fleece pocket diaps, you can use a free&clear detergent and should be fine. don't use dreft.
we don't have sensitive skin around here, so i just use the tide/kirkland regular detergent for all our laundry, diapers and clothes.
there are discussions galore about how to wash/what to wash in on the diaperpin.com boards
>5. Aren't polar fleece covers too hot for summer, will they cause rashes? (I am allergic to wool so I think I'll avoid using it with the babe.)
i didn't have my sugarbums polarfleece cover in the summer but it's a pretty light fleece - it's malden mills windpro. i don't think there'd be a problem with it in the summer.
>6. Is there a brand you've had good or bad luck with?
i like everything we're using so far. the ME one size were way too big on milo until he was about 4 months old, so i don't know that i'd truly say they're one size fits all. i *could* have used them, but they were way bulky and no clothes would fit over them. i really like the happy heinys - i had some poopy blowouts with them at first but it's 'cos milo was still too small for the mediums when i ordered them. since he got a bit bigger, i've had no problems.
good luck! babiesinthesun.com has/had a sample package where you can get several different types of diapers to try 'em out.