.$2500 seems high...not sure on sizeFlooring seems high - not sure on size...regional flooring companies in my market are very affordable and reliablePlumbing and electrical - I don't have plans to re-plumb or re-wire units every 20-30 years but do include estimated cap ex for fixtures.Off topic but consider LVT rather than laminate wood...it's very durable and can get wet.  

It was, build in 1978 which is an extremely average age for a conforming multifamily in Stockton.

For the size of you project, I'd make sure you get a 9-12 month hard money loan. 6 months won't be long enough.

average rent for the lot is 900/month.  

By looking at comps on the market that are similarly in size, upgrades or not, basement/ no basement, garage, backyard size, etc it can help you price out the property you're scoping out to re-sell or rent.

In addition to the price ask how many bedrooms, bathrooms, basement, attic, pool, deck, size, rent (if it is multifamily), location (how close to beach, transportation, job), updated or outdated appliances or cabinets etc the house has. 

I don't think there is a baseline average, I think it matters who your investor is and what your current relationship entails.

There is no way the casual investor is going to attain the average rental yields he does,  nor have the ability to call up a contractor and get a first rate, immediate response at wholesale contract prices so if it is a pain for him, it is worse for everyone else.There is absolutely no question the casual real estate investor can buy at full market value in Houston, in the decent low valued neighborhoods, and get cash flow and yes, long term wealth as long as they can get the low interest conventional loans. 

8 percent for vacancy(national average) unless you know the actual vacancy rate for your area (which you should definitely learn), 10 percent for maintenance and 10 percent for capital expenditures.

I have done some decent size deals, and the bigger the deal, generally the longer it takes to get done.