I'll save $5k in developer fees by waiting but will have yo solar PV the ADU;maybe do the sfr at the same time.

., and how to maximize savings and write offs. 

Me and my friend have lived at home for more than a year and have saved up enough money to buy a house and move out. 

It could be very advantageous and save you thousands on commissions and having access to the MLS is very helpful as well.Having access to properties without having to wait for an agent is priceless.

I'm waiting for the @Chad Carson Retire Early with Real Estate book to become available on Audible.

Using only these assets and liabilities, John's net worth has increased from $125K (SFH1, no debt, no savings) to $150K (SFH1 + SFR2 + savings - LOAN). 

I have saved up about 225k in cash and another 230k in stocks consisting of 401k and iras of with I could pull out a total of about 150k of.

I am starting out in REI, but I have a hard time imagining not maxing out retirement accounts available to me (403b, Roth IRA, etc). 

Strongly suggest you to use the BiggerPockets Calculator as well as look into Lease Options as that might be another exit strategy to save on the repair, hoa, property manager costs. 

He's a smart business owner who "retired" a couple years ago and is now starting new ventures.