Getting pre approved is very important. I don't like to take out buyers without a preapp. There is no point in looking at houses if you can't qualify for the mortgage to buy one.
You can ask your agent for reccommendations, or contact your local bank that you do business with. I can also give you some info, if you contact me through my website.
You will need to prived basic information, income, debt,etc and then the lender will tell you the maximum amount you qualify for, based on your downpayment and credit history. That is just your guide. You know how much debt you are comfortable with, so then you decide how much you mortgage.
Being pre approved presents you as a serious buyer to any seller.
Good Luck in your home search.