Real Estate Advice

[Sheriff Gonna Getcha]

So I'm buying my first home within the next few weeks. I've done a TON of research into the housing market (particularly mine), financing options, etc. But I've still got a few questions and, given the number of highly intelligent and successful people on this site, I'm looking for advice from some of my warpath brothers.

First, is there any sort of generalized formula for determining whether a house is a "good buy" based the home's assessed value?

Second, to what extent are buyer's agents useful? I know that buyer's agents owe fiduciary duties to their principals, but do such duties actually compel the agent to do what is in the principal's best interests given that their commission is based on the home's purchase price?

Third, how many home inspectors do people typically retain? Is there any way to determine if a home inspector is qualified, other than asking friends? For example, do they have certifications that might indicate that certain inspectors are more qualified than others?

Fourth, what is a good percentage of your gross income to spend on mortgage payments (including escrow)? I know this percentage will vary based on the individual and his outstanding debt, but is there a range for the "conservative" buyer and the less risk-averse buyer?

Finally, what kind of "hidden costs" can I expect to incur? Obviously there is the down payment, loan origination fee, and inspection fees, but what other fees can I expect to pay?