It might a better idea to target a house hack multifamily property for your first investment in order to learn the financing, maintenance, and tenant management aspects of the real estate industry and get comfortable with those prior to adding on learning about permitting and construction on top of those as well. 

Do you know whether there are significant barriers to adding a large tent long term to a property in J Tree if we were to set up a glamping spot?

Its not bad, better that not having one but if you want to fast track do a little bit more work upfront to get to freedom faster you'll likely want to ad value to a property forcing appreciation and raising rents

Talk to an expert like @Dave Foster but my starting points would be…What’s the upside to adding your son?

Even down to adding it to the contract and turning it into the title company how can I go about doing this.

Any financing will need to be other than F/F.In the case where the F/F rule against financing a multiplex with an ADU is enforced, adding 2 ADUs is similar to adding 1 ADU because in both cases the traditional F/F financing is unavailable.I suggest you have a discussion with a lender that you trust before adding a ADU. 

Any Animal that is considered a venomous or poisonous species is prohibited.

Looking forward to adding value to this community

Then move on if you want to adding a second asset class or strategy ONLY after you have mastered the first.Don't do a little of this or that.

Great comments Ohio Realtor.I just wanted to added in that it is all about "disclosure".