The 620 FICO score applies to FHA-insured financing. 3.5% is the minimum down payment. Overall, you'd probably need somewhere between 6% and 8% of the selling price to complete the deal. To qualify for conventional financing, your score would need to be at least in the mid-700's, with a 5% down payment. A little more cash would be required to purchase the home.
The property in question appears to be a foreclosure. Most are best suited for investors, since they're sold "as-is, where-is, with all defects." There is no Seller's Disclosure, no repairs will be done by the lender, and generally no allowances will be made for condition ... it's yours as it stands. For an owner-occupant, it's rarely a good choice.
You would need to meet the criteria established by the lender/owner, although you wouldn't have to use that institution. The listing does not indicate that the FHA route would be viable in this case ... it shows cash or conventional financing (with proof of funds) as the only two options.
As you can see, real estate transactions are not the cut-and-dried processes they appear to be, especially to first-time buyers. In addition, considering the fact that there is no cost to you as a buyer, the services of an experienced, professional Realtor can only work in your favor.
I'd love to further discuss your situation with you. Please feel free to contact me at (713) 213-6350 or ... email@example.com. I look forward to hearing from you.