Every new band needs a place to practice. I know I've practiced in garages, bedrooms, basements, living rooms, hallways, and even written some acoustic stuff on a train bridge and on the edge of a cliff. Anywhere your comfortable (and let me stress the word comfortable) can make a great practice spot. Being comfortable is important though, especially for a vocalist. Any stress can throw off their game, and practicing for the first time with a new band in front of your extended family can't help. Distance is also a big problem. Most bands contain between 3 to 5 people. If the practice space is hard to get to for even 1 person, it will throw the whole band off.
In my opinion a serious band should practice at least 2 or three times a week. I've definitely had a few side-projects where there was only time to get together once, and it worked fine; the downside being we wrote less material in a longer amount of time, and we constantly forgot the material we were working on. Trying to answer how long you should practice is another story. I've had 8 hour practices and 2 hour practices, and each one works for different types of people. If your band consists of guys who can jam for 8 hours straight and not loose a creative focus AND still have fun with it, then go for it. Not many people can do this though. The rule of thumb is, practice for as long as it takes you to feel like you have accomplished something. If you can get it done in 2 hours, go for it! I always bring some type of mini recorder with me just so I know what to work on for next time. Not having to MEMORIZE things during practice definitely helps to keep everyone in a good mood.
A few side notes. You should practice how you would on stage. Drums in back, singer in the middle, and guitars on the sides. Thats unless your writing your own music. If your writing, you want to turn everything down so that you can hear each part clearly. If the music doesn't go together soft, then it won't go together loud. This just helps to keep everything more controlled and keep frustration out of the picture. Also, Everyone should practice their part in their own time... Your band won't stay together long, if a few people are working hard for it and your just riding the wave.
Once again, let me know if I missed anything. I'd be happy to update!