Do all the figure just 'get reduced' by 20% (the amount of the second)..... meaning use a purchase from of 120K, depreciation of 40K and capital gains of 80K?

If you are reasonably confident your original filings are solid (beyond the depreciation error) then why not amend for something you were clearly entitled to, and in fact must claim since your tax basis in the property will be reduced whether you claim it or not.

And the note assumed by them would reduce the cash into the exchange account. 

The insurance companies know if you take ACV instead of RC, their claim payout gets reduced by 25%-50%

Make sure you try to turn the handle before you turn the dial. 

They key thing is to use an escrow company that you trust (since they will be handling the cash) and also make sure you trust the realtor you're working with. 

- Does the IRA provider have the capability to handle my IRA if it wants to extend a line of  credit?

Person A and Person B would like to sign another year long lease, although Person C is only looking to stay until around June or so, at which point he'll move out and Person A and B will have a new roommate move in, who would be Person D.This is all fine by me.However I'm not sure how to handle the lease renewal. 

He also stated that the charge to handle the exchange is a flat fee of $850, which I didn't think was too bad.

My thoughts are I'd rather not start off with an eviction, but don't want to go 8 months with such significantly reduced rates.