Monthly payment uses the amortisation formula M = P[r(1+r)ⁿ]/[(1+r)ⁿ-1], where P is the loan principal, r is the monthly interest rate and n is the total number of months.
Most lenders require 5–20% deposit. A 20% deposit avoids private mortgage insurance (PMI) in the US or lender's mortgage insurance (LMI) in Australia and typically gives better interest rates.