If he contract with the seller gives a closing date of on or before- 30 days from execution of the contract, and if I find an end buyer and would like to close sooner- do I need to do an addendum for a-b contract to modify the closing date? 

Yes, always execute a NCNDA when brokering.

Avoiding building permits makes you vulnerable.

An executory agreement still requires unilateral cooperation and requires an additional "next step" before the agreement is fully executed.

You must constantly stay on guard against the “slicksters” who expound on softer, easier and faster methods that will make you rich, I have discovered this vulnerability in myself.

Lastly, what about rental agreements can the existing owner rental agreements with tenants suffice or should I execute new ones? 

Then when you execute your option to buy, the purchase price will be commensurately lower since you would have had some portion of rent payments reducing it.Another option is not to do a MLO, but to do a land contract.

I don't have real estate experience other than reading a lot of different strategies with never executing on them for one reason or another. 

As a veteran I get asked some disgusting questions about my previous profession even by executives interviewing me so I have found ways to get around them.When I get asked how many I own, I respond with a humors "enough to keep me busy" and laugh it off. 

To me, this level of planning, due diligence, and detailed analysis/unerwriting of all of these considerations is one of the major things that separate the newbies from the pros; the ability to execute such plans is the other.