@Moazzem Hussain The reason why a lot of investor don't work with the big banks is that their underwriting is often time more conservative and they usually stop issuing loans after 4 loans. For the investors that are trying to max out the fannie/freddie loans (10), they would need to work a different bank that will do them. So why not build the relationship earlier on?
It'll depends on appraised price and your DTI ratio. Most banks will do 30% DTI, the advantage of having the other units rented out is that the bank will use the rental income at 75% and add it to your income to decrease the DTI. For example if you make 6K a month, Banks would usually want to keep your payment for your debts at 2K so if you are already at 1700 with your house and car, there is only 300 dollar allowance for this new debt. However if you are able to rent all your units out before getting the refi, then you can add 75% of gross rents to your monthly income and it may open up more room for your loan.
The actual percent doesn't really matter, you can pay points to get it lower. The percentage can be as low as you want by paying more upfront.
Yes, comps are comparables, you can use Zillow, however only use comps that are within 6 months and like property within .5 miles if possible.