1. First, get copies of the lease and confirm when the lease expires, if they are month to month, security deposit info, etc. If the lease runs past closing their lease is still good and its on you. If they do move out, they will be looking to you for their security deposit so make sure you get that squared away with the seller prior to/at closing. Unless there is some requirement/law that prevents raising rent, it is a business decision for you. Screw their feelings about what they feel the rent should be, but respect the lease until it expires. Why is the Seller giving notice to vacant after closing, its yours at that point. I wouldn't rely too heavily on someone who has their money already. I generally have the seller provide the property vacant or I want a further reduction on the price.
2. For insurance you are going to pay for the first year in total and prepaids for insurance, tax escrow. This is normal to me but yeah it stinks.
3. Dig into the details of the closing costs and have the lender explain each one. Don't stop asking until you understand fully.
It looks like you are going to be spending approx $325K - $350K on this purchase all costs included for ~$2400 in rent at market value. I don't know the projected operating expenses or potential appreciation, but it doesn't look like a screaming deal on the bare surface. I could be wrong. Sometimes the universe is telling us something.