How are you finding your listings? When you meet with the realtor, let them know you want automatic MLS (multiple listing service) alerts to come to your email based on your parameters. You will get an alert the moment a house is listed for sale, while many websites are delayed (and thus the deal is gone).
50% rule is on your rental income, not purchase price. Annual rent increases depends on the market more than anything. It's easy to optimistically assume, but you have to be realistic as well. Are you taking into account PMI, taxes, property management if you go that route, etc.?
Keep in mind I have no personal experience, this is just what I've learned from BP, podcasts, etc.