There is also one big issue with your tax projection - the taxes of $280 are based on the vacant land taxes and will likely go up to ~$2000-$3000 in a year or so when the assessor catches up with you.I realize there is a 1031 involved so a real estate purchase is necessary, but you should compare your ROI to a safe yielding instrument like a 10 year T-note or AAA corporate bond yield. 

I feel deeply obligated to make sure the seller's credit is protected as they trusted me personally to make sure bad things don't happen. 

If something really bad happens,  the lawyers would "Pierce the corporate veil" of those LLC's to get to your assets anyway. 

It just looks like another corporate guru trying to win your business.

Estate is not obligated to honor it. it .. but check with an attorney there this is an easy question to get answered.

The only reason I'm hesitant to move forward without this info is that the seller is an inactive corporation - if they dissolve and there are issues with their warranty deed then I don't want to have to pay a lawyer to go after the GP of the defunct partnership to make me whole.

This means that you will probably need to pay registration and filing fees in at least 2 states if you don’t buy CA property as a CA resident.Any lawsuits should be limited to the assets of the LLC and not your personal assets (assuming you run the LLC appropriately and the corporate veil is not pierced, some debate as to SMLLC).

YOU make the decision on what it sells for NOT your realtor.. if it does not sell for listed price your under no obligation to sell.. 

It states clearly in the lease that they're obligated to pay an extra amount, so I think a $140 amendment to the lease every month is reasonable. 

If this is a large corporation it may make a difference, or if the landlord was that bad and a point needs to be made, then maybe.