I frequent play by posts a lot and to your questions.

1: The ones I'm in, conversations actually go by pretty quick if you're with someone who's on frequently or you can adapt to his or her schedule, and if the forum reaches post cap start a new thread

2: This mainly depends on the users but most of time they might hold the RP up for you group to catch up (this however is how one user can kill an RP if it's held off for too long so YMMV) other solutions involve flashback and if all else fails, evoking the MST 3 Kmantra

This is something a friend of mine wrote up a long while back. It may be of use to you:

What are Play by post rpgs? Play-by-post role-playing games fall into the category of online text-based rpgs; the first type of rpg to grace the Internet. They borrow some traits from both interactive fiction and collaborative writing to create a fun activity for those who are both gamer and creative writer. They have about every setting out there you can imagine: game-based (Resident Evil, Final Fantasy, etc.), book-based (Twilight, Harry Potter, Lord of the Rings, etc.), TV-based (Star Wars, CSI, etc.), and there are myriads with their own original settings and plot as well.

How does it work? Play by post rpgs most commonly take place on an online forum, though there are several other ways to do them as well (email, chat rooms, blogs, etc.) The forum has a decided setting and general plot (for example, Russia in WWII) that players are to implement.

The first step for every player is to create a character to use. Every player's character has their own personality, visual appearance, and past (though some forums, such as ones based on a book, game, or TV show, have premade characters to choose from). An experienced role-player will avoid making Mary Sues/Gary Stus, or idealized characters without any noteworthy flaws/weaknesses (e.g., a skinny, big-breasted blonde woman with an endearing personality and a lot of money), because, let's face it, this is detrimental to the other players' enjoyment of the game. Invincible, perfect, extraordinarily lucky, or otherwise over-powered characters is considered godmoding, and as such is intolerable at most play-by-post role-playing sites.

After character development, the game begins. A player can either start a thread or join an open one that another player has already created. In any case, the thread-starter is usually that particular thread's lesser gamemaster, meaning that they lay out the time and setting of the thread (such as midday, summer, by a lake in a forest) and are solely responsible for changes in the setting and time that take place in that thread.

From that point on, the thread becomes something like a collaborative story. Participating players take turns posting the actions, dialogue, thoughts, etc. of their characters in third-person format. When a player controls another's character it is called powerplaying and is looked down upon at every reputable gaming site on the web. Avoiding consequences that the environment/other characters would normally have on one's own character is another form of godmoding and is illegal almost everywhere. A good role-player will avoid godmoding and powerplaying at all costs.

Where to find them. Play by post rpgs are all over the Internet, and there is such a vast variety of them that linking one or two would be unfair to you, as well as the rest of the text-based rpg world. It all depends on what you're looking for. My first suggestion is, naturally, Google. Yeah, it's that easy. Type what sort of role-play you want (some examples are medieval fantasy, The Golden Compass, or superhero) followed by Pb P rpg. Some other good links are Proboards and Invision Free. Both are companies that offer free forum hosting for gamemasters and they both have extensive directories for role-players to dig through.