In order to build wealth and make money work hard for me,I am thinking about how to use the equity I build.After I purchase the property,if the refinance LTV ratio is 70%,the value of property should increase about 40% to refinance all the capital invested in the property.And if the property appreciation compound annual 10%,it need take more than 3 years to get 40% increase.If the property does not appreciate a lot,the refinance does not worth it at all.So I need to use the capital I invested in the property more than once,I need to choose the property which has al lot of property appreciation.Anything wrong about my math?

With that math I am seeing that my property should be worth $280 -$300k when I am finished and fully occupied.

If you've done your math, added all of your safety margins, made an offer, and the deal doesn't work out, on to the next!  

Currently if I work overtime I get paid 1.5x base pay, but I am wondering if someone can help me with the math of what I would roughly be making (1.4x, 1.3x etc.), since I would also be lowering how much I could write off the above rule (my OT wouldnt be extensive enough to have my income >$150k).

Just a little error in your math.  650-447.5=202.5 not 252.5.  

Do the math. 

Do your math to find your cash flow and don't worry about the "rule" 

All the best math and planning, but still never know who your neighbors could end up being!  

One point I was going to add is that to figure out which way is better is to just do the math. 

I don't have calculated statistical data to back this claim up, and it could be regional, but it often seems that appraisers are more generous when it comes to appraised market rents than they are when it comes to value.I'll not bore you with the math, but the arithmetic is more generous if you do not intend to live in the property than if you do intend to live in the property (If you aren't going to live there, it is in theory possible to have a calculated DTI of 0.000%... which is in part why commercial financing uses DSCR not DTI).