Although I have already read about the laws related to security deposit matter in CA Civil Code Section 1950.5, I would like the property owners with similar experiences to me consider my situation and advise me regarding the following items1- How to calculate their security deposit and provide an itemized list, while I do not have any invoice in my hands. 2- As my tenants have not left any forwarding address, shall I contact and ask her the new address for sending the itemized list?

That should help insure some sense of priority and trust to find the right "investment." 

There are a TON of deals I've done where if I used the 70% rule I would have never considered the deal yet they made me 30k or more.One of the most trusted investors I know who is making 100k a month in passive income has a rule of $200 per door and 10% maintenance/management, insurance cost etc...Write out the numbers and see what it comes out to.

Thanks  Paula, it feels good to know that I'm not the only one who has put to much trust in a Contractor. 

Trust yourself and don't let other people's valuation sway your decision.

So lesson learned- now rifi, move on, and next time get an inspection and/or add language in your contract that addresses this type of potential issue.

Also, do I just write the landlord/subleasor a check with the property address and month on the check as payment?

I'm asking because from a few hours of googling around, it seems like the numbers across website are wildly different (I've seen from ~5% to 10% for the same exact zipcode), and I'm wondering which ones the veterans trust?

There is not a defined percentage of time you must occupy the residence so long as it is your primary residence and is used as such (you get your mail there, your license has that address, etc).

If you can come to terms with a Seller, you definitely want to engage either a title company and/or a real estate lawyer to ensure the transaction is executed correctly, the deed, deed of trust and promissory note are all drawn up correctly and filed so that both parties are protected