once a month is sufficient? 

Set aside enough for a 20% down with sufficient reserves.

We think it’s important as it allows us to check for Non-Sufficient Funds (NSF) issues and to determine if an applicant is living paycheck-to-paycheck.

The current lender could appraise the smaller parcel and perhaps determine the collateral is sufficient.

Wethink it’s important as it allows us to check for Non-Sufficient Funds (NSF) issues and to determine if anapplicant is living paycheck-to-paycheck.

I recommend you do some market research on the price points to purchase and what you can get for rent to answer the question yourself.Regarding a 3 to 4 unit, If you decide to use an FHA loan make sure you research the FHA self-sufficiency guidelines. 

Since you're purchasing your first home, you likely don't have this rental history.Lease Agreement: While a signed lease agreement is a positive step, it might not be sufficient on its own for a lender to consider the rental income in your mortgage application.

I did not know that triplex/fourplex would require self-sufficiency test.

Regarding not good credit, I usually request a co-signer and copies of their bank statements showing that they have sufficient reserves in case anything arises.

Typically in California, a Will alone is not sufficient to avoid probate - which is a pain, time consuming, and very expensive.