Investment properties require a much different mindset than do primary homes. On a primary home, there is an emotional component to the purchase. Specifically - "Am I going to be able to call this a 'Home'?"
On an investment property, you must take out the emotional component. It's all about the numbers.
With that said, come up with an outline of what you want to do. Talk with a lender to see what you can be prequalified for and what that additional cost will be per month. You need to be comfortable with it. While you are coming up with your outline, talk with a good realtor that has experience with investors to help hone your outline into a plan of action.
In your research, you shouldn't have to think -- can I afford this property. You will already know that based on your meeting with the lender.
Your primary decision should be -- can I get my target rent out of this property? Will my expenses be in-line with my plan?
Short answer - talk with a lender very early in the process.
Timing is always a toughie. On one hand, it is always good to know the market. Whether you are looking for a personal home, or an investment property, you need to know what homes in your target areas are worth when they come on the market. That is the only way to spot the ones that are well priced for your needs.
Starting too much before you have the other pieces in place can be very detrimental. If you haven't looked at financing, and you start looking at homes in the wrong price range, may find that qualified properties are underwhelming... or overwhelming.
Starting too late, especially with a personal property, might mean that you don't have enough time to really feel the market, or wait for the right property. Usually investors have a more flexible attitude about when they can look. It isn't a need, but rather an investment, so they can take the time to do it right.
I would say that in the case of an investor, it isn't ever really too early to look, after you figure out what you are in the market for. For personal purchases, figure out what you can buy, and then start looking 60-120 days before you wish to make a move. The more rigid you are in what you want to find, the longer your horizon needs to be.
