I just think $3000 is a bit excessive.

For example how much excess cash do you have each month that you can save up in order to invest?

You may wish to confirm that the new 401k provider will handle the ongoing compliance support such as any required 5500 filing (e.g. 5500-ez for a one-participant plan with assets in excess of $250,000), any required tax reporting (e.g. 1099-r in the event of a distribution or in-plan Roth conversion), mandatory plan updates and amendments, etc.4.

Here is an excerpt from an article on the subject that I believe breaks this down fairly well:Gain, to the extent of the depreciation claimed that exceeds what would have been allowable under straight-line depreciation, will be recaptured as ordinary income, and, thus, taxed at rates as high as 35% in 2003 and later years (ordinary income rates), but the amount of excess depreciation subject to recapture may be less for certain low-income housingGain, to the extent of the depreciation that isn't recaptured as ordinary income, will be taxed at a rate of 25%.The balance of the gain will be taxed at a rate of 15%Example – In January 1986, you paid $1.3 million for an apartment building (not a low-income building), of which $1 million was allocated to the improvements.

For instance if you let the value of the land act as the equity for the seller then you will need to bring the excess cash or at least have the balance sheet to cover the difference for the lender.  

California charges a minimum tax of $800 a year per LLC, and more if you have gross receipts in excess of $250k.

Usually about monthly, I transfer the excess cash to a savings account.

15% profit with all of the unknowns and risks is not excessive. 

If the value is more than that, the excess reduces your parents lifetime gift limit.  

If you discover the repairs and removal are excessive you can communicate your concerns to the seller in the form of a new offer at a lower price OR request that they remove the tank prior to closing.