The numbers you have given make this look like an awesome project. I came up with a 50% return on your money assuming $125,000 down. A lot of the big boys in my area are looking for 15%-25% return. Seems too good to be true.
My next steps would be check the financial health of the tenants. Most of their leases expire relatively soon, definitely worth a look to make sure they'll be around. Why are they selling this property? I would get all of the various receipts for the items the seller is giving you (rental receipts, PM receipts, tax records, etc) for at least the past three years. Seeing that you confessed to no experience with commercial, I would run these numbers by your CPA and commercial lender to determine their validity and liquidity. What sort of condition is the building itself in? Are there any big ticket capital expenditures coming up? Get records of maintenance for as far back as you can get. What is the overall economic climate of your community? Speak to the property manager at length about the building and tenants.
Sorry to throw a million different questions and ideas at you, but at this point, you have to:
a) verify that the numbers provided are correct
b) find reasons not to buy the property
As harsh as it sounds, if you can't argue against your project (buying the property), you do not understand the project well enough to proceed.
Best of luck and keep us updated as you go through your due diligence. It sounds like this could be a real winner!