@Tracy Scott it's highly dependent on the deal, the type of property and the location.In addition to the items others have mentioned, here are some of the biggest potential start-up expenses that I study closely before buying a property:Foundation/structure--this is one of my few "deal breakers", I typically will not purchase a property with significant foundation or structural issues.

The fact that you want to get started and take action is already half the battle and as a long time listener of the podcasts I'm sure you already have a good foundational understanding of the basics.

I am an experienced renovator, having done work and management on all aspects of my own properties from the foundation up for 18 years.Since the State laws are new, I'm excited about the possibilities, and looking to chat with other Owner/Builders about the feasibility and pitfalls.I guess that my biggest open questions are about foundations and waste water management requirements in conjunction with an existing multi family building. 

I know the general basics of the market, the business model, etc, but I was hoping to take my knowledge to the next level.My biggest goal right now is to own a rental property before I graduate college (currently a junior in high school).For context, I love reading books about investing and personal finance (I have a very solid foundation of knowledge built up) and I currently have a portfolio of about 11k between stocks and crypto. 

I would venture into markets in the mid-west, build a solid foundation, and start doing the BRRRR method.

We basically build our foundations on mud and clay here so movement is inevitable. 

You don't need to know everything to get started; you need a foundation to build on and the rest will come through experience and then refining your education.You can build a basic understanding of investing in 3-6 months.

We NEVER had a problem with mice chewing the plastic (over the last 12+ years).One method of keeping the lil critters out is to parge around the foundation on the outside. 

Yesterday, I posted my standard notice on the front door advising the occupants that the place has been sold, to call me, and that if I don't hear back, I may initiate an unlawful detainer or if the place is vacant that I may change the locks, along with a copy of the deed.The property looks barely habitable (hot water heater is on the back porch (which looks like it's about to fall off its rotted post foundation), sheets of drywall and plywood out front, tons of beer cans and collection notices on the front door, and rotted siding/wood on one side of the house.

If you're planning on building an ADU or JADU 'yourself', my suggestion is to make sure you have some previous knowledge of construction and also make sure you know good sub-contractors in the following trades:  electrical, plumbing, foundation, roofing, framing, drywall/paint, stucco, tile, cabinetry, flooring, HVAC, concrete, etc.The last thing you want is poor quality work that has to be re-done because a handyman or the wrong tradesman did the work.