The price drop of 20 - 30 % seems particularly high jusm ? Can I ask just an approximate general area ?
On Equity , and assuming your valuations are bank valuations ( eg : marketline ) , and the income levels stack up I cant see that you will have any problem .
Agreeing that you are taking on a fair amount of debt , make sure you are comfortable with that amount , and make sure you can easily service it should anything go wrong . The rental income would of course be taken into the equasion , your viable rate sounds okey to me , but others will be able to tell what the best viable rate is .
Personnaly I would use a broker , but check out all alternatives is generally best , such items as deffered establishment fees , and account keeping fees must be considered .