Then there is the time to negotiate the new lease(s), preparing space plans for the new tenants needs, preparation of new working architectural drawings, typically 30 days for a building permit, demolition cost and time to remove the old improvements, and then 30 to 90 days for new buildout and occupancy. 

The problem is, each city is unique in the amount of time they take to process for permits, some cities do in house others farm out plan checks, etc.

Seller will convey the Property to Buyer at Closing with marketable title in fee simple by transferable and recordable general warranty deed, with release of dower, free and clear of all liens, encumbrances, conditions, easements, and restrictions, except for: (i) those of record which do not interfere with the intended use of the Property as a permitted use under the current zoning for the Property; (ii) those assumed by Buyer; or (iii) those which are open and notorious or which could be determined by a visual inspection or survey of the Property.

if you can get both figured out to your satisfaction you talk with your renter and make sure she gets any special permits or insurance needed to protect you. 

Any non-permitted modifications will also be reverted on the owner's dime (or the owner fined until they do)Probably completely different in LA, but not something to mess around with until you talk to someone well versed in your local rental code.

Since then I've been voraciously devouring the BP Podcasts while working out or driving anywhere, as well as watching the Webinars when time permits.  

You will need to do more research on the property as some locations now will not even issue a building permit if the grade is not above the 100 year flood plain, which this being an AE then It is not.

Just because the statistical data says a home is worth $212M, doesn't mean the house hasn't been gutted or that the 2,000 square foot add on wasn't done with a permit or that there isn't a crackhead living in the place right now using the furniture as firewood. 

Does anyone have a recommendation for a software to create a layout/drawing for my contractor to use for his permit request?

You need to find out if adding another home is permitted.