Personally, I would never get an ARM (adjustable rate mortgage). They're just too ify. Just about any Financial Advisor worth their salt will tell you that two of the worst financial decisions are ARMs, and vehicle leases. Best bet is 15 year fixed if you can afford it. If not, 20, 25, or 30 fixed would be my next choices. Chances are that after you are in the house for a year or two, you can start to increase your contributions to the principal amount of the mortgage and significantly reduce the term over the long haul.
Many homeowners are starting to realize that they don't necessarily get their moneys worth from listing with a realtor and are selling on their own. Don't be afraid of buying this way, just make sure you have an inspection done - which will be required by the lender anyway. Or, you can represent yourself and deal with a sellers agent. If you're really not comfortable with this, especially for your first time, go ahead and find a good, reputable agent, but pay attention to the process so that you realize how easy it is next time around.
One rule of thumb is that your mortgage payment should not be above 25-30% of your take home pay. For some, this may be uncomfortable, and for others, they may be good enough with budgeting and avoiding other debts, to go higher on this. It comes down to what you are comfortable with - and be honest, and also what your lender will give you.