You're welcome to take a look at our services for WordPress Hosting.
But let me see if I can add some to the conversation here...
First BlueHost, even through they are our competitor, is a real hosting company - I wouldn't take that away from them. One of our customers did have issues with them though. You can read her testimonial from our site's sidebar when you click on a link like our blog or some other page.
She had the same issue with them - CPU overages and they locked her out from her site.
Here's the thing, though. Shared hosting is a starting point for website owners and bloggers. It's inexpensive and easy. But when your site gains more traffic and starts causing a load on the server you are on, it's time to move up to other hosting options.
Look at it like this. If my site started receiving tons of traffic and started taking up 30% of the CPU time, your website (if hosted on the same server) would start running very slow because it has to wait for my site which is hogging up all the server's resources. Now imagine if there were 300 websites all hosted on the same server all requesting tons of CPU time, no one's site would load quickly - no matter what caching program you use.
So this process of monitoring and limiting CPU usage is a protection for you from other sites ruining your blog's performance.
If your site is consistently going above say about 5% CPU time, it might be time to look into Virtual Dedicated hosting. You'll get more CPU time and resources. It's more expensive, I know, but shared hosting has its limits.
1. Not sure about which plugins work slow, but I do know if you use too many it will slow things down. Many people use the FeedBurner and Google Analytics plugins. Those aren't really necessary as you can easily paste in the correct code without a plugin.
2. Most hosting companies start around 4% or so. Our company doesn't put a limit on it, however, we monitor for problems and then notify people if issues with the server start to arise.
3. That's impossible to answer as everyone's site is different. For example, you might not have tons of traffic but perhaps you have tons of streaming video hosted on your site. If you get too many people streaming video all at once, that could put you over. As an example though, one of my blog articles hit the front page of http://del.icio.us on a Saturday night and my CPU usage went up to 5.5% for a few days as my traffic spiked. If you have a blog with just a few commentators, you might be looking around .4 - 1%. But again, hard to tell because it depends on a lot of things.
4. See #1.