There's a FAQ at the top of the board with some good stuff in there.
1. How many do we need? If this depends on what type we are buying, can you give me an example?
It does depend what type you use but you will need enough for probably 8 changes per day, at least, with a newborn, reducing to maybe 4-5 for an older baby. If you were using all-in-ones (no separate covers or anything) you would need 8-10 per day at first. If you wanted to wash every other day, you'd need 16-20 PLUS enough to use while you wash and dry them. Some nappies dry really quickly so you'd only need an extra half day's supply, but other nappies can take 2 days to air dry so you'd need another 16-20! So it really does depend. I would start by looking at when you want to start cloth nappying. If you want to wait a few weeks, you won't need quite as many as for a tiny newborn. Then look at what kind you think you'd prefer because that will influence it too - all in ones generally dry more slowly than nappies that come apart more. Then you can work out how many you need

Lots of people start off washing every day (it does only take a few minutes after all) and then reduce it as baby goes through less nappies per day.
2. Have you ever used flushable liners? Do they work well?
Yes and no, not in my experience. A young breastfed baby's poo is liquid and will either soak through or find a way around it! BF baby poo is soluble anyway so there's no need to dispose of poo, just throw it in the washing machine. As baby starts on solids or if you FF the poo won't dissolve so that's when you'd maybe want liners. I much prefer fleece or suedecloth.
3. If you don't use flushable liners, do you scrape the solids off with something or use a hose?
Once baby has more solid poo, I tend to give it a quick wipe with some loo roll to remove any solid bits! Some people rinse it under a tap, under the shower or with a 'diaper sprayer' but we don't tend to have them in the UK so I haven't used one. Once baby is doing properly solid poos, they just tend to roll off fleece liners anyway, no scraping involved! Don't be put off. Once you have a baby your ideas about poo change

.
4. I have heard that you are not supposed to use as much detergent with cloth diapers. Is this true?
Definitely. Too much doesn't rinse out properly and builds up in the fabric. The nappies lose absorbency and bacteria gets trapped, leading to stinky nappies and maybe rash. I use 1/7th the recommended dose (perfected after much trial and error) but I'd generally advise that you start with 1/4 the normal dose. And do extra rinses.
5. Do you use disposables when you go out/on vacation? If not, how do you deal with the cloth diapers?
Nope. I did once for 4 days and my daughter got horrible rash so I vowed never again. I just take cloth with us, but we haven't been abroad. I still would, I think. 4 days worth of Flips (a very trim hybrid nappy) takes up about the same luggage space as a pack of disposables. I have hand washed in a bath of a place we were staying but it's better to only stay places with a washing machine!