Yes your credit score will usually determine the interest that you'll be charged by the bank and the information in your credit report such as your credit history of past account will usually determine whether or not you will be approved for the loan you are applying for. If your credit is less then perfect then take some time to do some research and work on rebuilding your credit or obtaining and maintaining a higher credit score. It will benefit you greatly in the long run, both personally and financially. In the meantime you can go ahead and rent, its not like renting is throwing money out the window right now, since real estate is mostly coming down in price. So while you rent and rebuild credit for a year or two however long it takes (depending on how bad your credit might be) the house you want to buy will be coming down in price and as soon as your ready to buy it you will be able to purchase it at a lower price with a lower interest rate which means you will have a much lower monthly payment making it much more affordable to you and you'll be much happier that way.
Yes, credit will effect your buying power--if you have poor credit, work on repairing it--also, it's in your best interest to consult with any qualified loan officer, and have your credit checked, as their scoring is often different--he/she may offer great suggestions on credit repair if needed.
Yes, your credit will affect your ability to get financing in order to purchase a home. Your best bet is the get an honest and credible assessment from a good mortgage rep. who can help you understand what you can afford, and if your credit is an obstacle make recommendations to get you on track.
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