B.,
I have a four-month-old daughter, and we have been cloth diapering her pretty much since birth. (We used disposables for the couple of weeks she had her umbilical cord, since the disposables had a special cut-out for them.) I will try to respond to all of your questions:
(1) The cloth diapers I use (and they are the only ones I have used, so I can only speak to my experience) are BumGenius one-sizes. I don't know if you are familiar with Cotton Babies, a store here in St. Louis that sells all sorts of cloth diapers, but they are an awesome resource for cloth diapers, and they have a nightly class once or twice a month (can't remember how often) that is for the purpose of answering your questions about cloth diapers. The people that own the store (which has a website: www.cottonbabies.com) make the BumGenius diapers I use, but they also sell all sorts of other brands. I LOVE the BumGenius diapers--we've had fewer blowouts in those than the few times we've used disposables (we've used disposables a couple of times when we've taken road trips). They go on just like a disposable diaper, and you use velcro tabs to close them. They aren't any more of a hassle to put on than disposable diapers are. However, they have an insert that goes in them that you take out when you change the diaper, and then you wash the inserts and diapers together, but you have to stuff the insert back into the diaper when they are clean. So it does require that extra step when you do laundry. You CAN buy BumGenius all-in-ones, which are just like the one-sizes, but then you have to buy different sizes as your child grows. The BumGenius all-in-ones do not have the insert that you have to deal with, so it saves time, but it ends up being more expensive since you have to buy more diapers. The one-sizes are made to fit from newborn up through the time they are potty-training.
(2) The only thing you really need to get if you go with BumGenius are the diapers themselves, a diaper pail, and good detergent. (The diapers require special detergent that is free of dyes and other chemicals--however, they have a large list of detergents that work, and we have found one that works really well that is also really cheap, so it's not more expensive than buying regular detergent.) However, my daughter isn't eating solids yet, so when she does and her poop is more solid, we may get a sprayer for the diapers, so we can spray her poop off into the toilet. (But that's just about a $20 investment or so--it hooks up to your toilet and makes it easy to clean off the diaper.) Now that she's only getting breastmilk right now, the diapers are super easy, because we just throw them direclty in the wash.
(3) We haven't had a problem at all with smell--we have a spray that we can spray on the diapers after we take them off, but we haven't really used it that much because it doesn't seem necessary. However, we only bought enough diapers so that we have to do laundry every other day, so that might be why there's not much of a problem with it.
(4)The diapers cost $17 a piece, so it was a larger initial investment, but we will end up saving a ton of money in the end. We bought 24 diapers so that we wash them every other day, and we spent about $400. Compare that with the cost of Pampers, which run about $12 for 40 diapers, and it's a huge savings. (Of course, there are cheaper disposables than Pampers, but we initially bought cheaper brands when we went on a road trip, and our daughter seemed to have blow-out after blow-out in the cheaper ones.) So $400 sounds like a lot up front, but we'll be able to use these diapers until our daughter is potty-trained, and we plan on using them for our next baby as well. Of course, you can also spend far less than that on cloth diapers, if you go with more traditional prefolds--my husband and I just paid for the convenience of using BumGenius diapers, since they are much closer to disposables (and are also more absorbent than other cloth diapers). If you go with cloth diapers, you will also have the expense of doing more laundry, but I still think we end up saving money. We was them every other day, and we only dry them for 30 minutes, and after that, we just take them out of the dryer and drape them around a couple of laundry baskets to dry the rest of the way, so it saves some money that way.
Anyway, I totally love cloth diapering my daughter--it has been great, and she has NEVER had diaper rash. (Another benefit of the BumGenius diapers, since they are made to wick away moisture so they're less likely to get diaper rash than with other cloth diapers.) My husband was the one who wanted to cloth diaper, and I am now a huge convert, because it's been such a great experience. I would definitley encourage you to check out Cotton Babies--they can tell you so much more about your different options than I can. And hopefully you'll get responses from others who have used other kinds of diapers.