I'm in the same boat you are - maybe a few years along. I log in here at WebmasterWorld to learn! Every once in a while, I can contribute something...
On the few sites that I run (I have a different day job), I always sign up for the longest term available if I have prior experience with that hosting provider. It's just a better deal, and moving sites is not my favorite thing to do. Lower price, less paperwork, less maintenance with a longer-term account.
Time to get on-line? In my experience registering a domain name and buying hosting space in a package deal, it took 3 to 5 days. Buying separately takes longer, since you have to get your new IP address from the hosting service, and tell the domain name registrar so they can set up the Domain Name Server. You can upload your site and begin testing as soon as you have your IP address if you use relative, rather than absolute links on your pages.
Rip-offs? Stay away from any hosting service that won't give you enough control to block bad robots. For Apache/Unix hosts, this means you need .htaccess with mod_rewrite enabled. For IIS and other servers, this means your control panel must allow you to block access by user agent, IP address, and referer at a minimum.
There are a lot of "resellers" out there. They buy bandwidth and disk space in bulk from major providers, and re-sell it by running virtual hosting programs on the server. In general, the measures they must take to prevent their users from interfering with each other's sites limit how much "power" they can allow you to have in controlling your server environment - That's a problem. So, I prefer to go with the companies that actually own and administrate their own servers. (I hope I have stated only the truth here and don't offend any resellers who are present.)
Exactly when you might run out of bandwidth is dependent upon how much you are allowed, and how much you and your users consume. And don't forget all those e-mail harvesters, site downloaders, and search engine robots. If you don't control which of them can access your content, you can easily lose control and quickly go over quota. It might happen on the 28th of the month, or on the 2nd! That's why I insist on the hosting provider giving me the tools to deal with this issue.
A good rule of thumb is to guesstimate your need (by looking for competitive sites that have "hit counters" on them, and looking at their page sizes). Then double it. Then double it again (and maybe once more) to be safe. Like I said, better to pay for too much bandwidth at first and then scale down than too pay for too little and get cut off mid-month. (This does argue in favor of a short-term contract until you get used to these ideas.)
I don't want to violate the WebmasterWorld TOS by posting my personal preferences, but there was a thread here within the last few weeks about web hosting services - do a site search for related terms.
I hope I answered most of your Q's well enough to keep you busy for awhile - It is time to retire in Texas...