I know most stuff like HVAC repair, plumbing, and electrical should all be hired out by a professional but what about minor things like this?

I currently work for my brother (also an aspiring REI) doing residential Electrical work in Charleston, SC where we drive all over and often have long discussions about REI and the futures we hope to have with it.Now before y'all start yelling at your computer screen saying that "REI is a broad topic, do you really know what you want to do?!?"  

Ask them if they see how selling with a realtor 6-10 months from now will net them a 12-15% reduction, and if they say yes, then present your subject to offer as a means to save them time and energy.

Especially in LA where you can find people in good situations that may not have the time or energy to get the most out of a property. 

They also upgraded the electrical service.

My brother is wrapping up his PhD in Engineering (Computer and Electrical) but his girlfriend just moved to Boston so he is thinking about going too  

Regarding hidden costs, I would say electrical and plumbing.

4 plex right off busy intersection and <1/4 mile from interstate ramp.2bd/1bth 2bd/1bth 3bd/2bth 1bd/1bth4 Parking spaces (2 covered) + 4 street parking spotsPurchase Price 325K; 25% ($81,250) down conventional 30yrMonthly Mortgage Payment = ~$,1250-----INCOMEFully occupied, rents are $2825 combined.There is a shared washer/dryer room, listing claims ~$250 income a monthTotal Income w/ 5% vacancy factor = ~$2,900/ month-----EXPENSESProperty tax + Insurance + Water + Trash + Electricity for common areas + Landscaping + $200 Miscellaneous Repairs/Expenses = ~$1,000/ month+ mortgage payment = $2,250-----Yes I know, price is very high.

Price: $150,000 (planning on 20% down) Rent: $3,100/month (4 units at 550/month and 2 garage units at 475/month)Utilities 1,450/month (Owner pays utilities, electricity, water, gas, for 2012 came out to $17,000)Mortgage: 750/monthTaxes/Insurance: 450/month (based on zillow)Cash Flow: 450/month (please let me know if I'm missing some basic expenses)Building has window A/C units.

The replacement of a roof, carpets, air conditioning and heating equipment, appliances and other electrical or mechanical equipment, wood decks, parking lot, and so forth.