Imagine you are the mentor of an 18 year old kid that wants to get into real estate investing but has ZERO credit history.. 

Pretty much the position I am in.. No authorized user options available.. What would you recommend to them?

How many accounts and what accounts would you suggest for them to get on their reports and get them ageing in order to set them up with the best possible credit profile so in the future they can get approved for the best rates on Mortgages, refis, helocs, improvment loans, etc.? 

So they will be able to BRRRR and carry a mortgage on 10 rentals while still being able to finance more and everything you need to do to get rich investing other peoples money in real estate..

Get lots of accounts on there? Just a few? 

Should they also fire up an LLC or similar as early as possible to get their business credit building as well? Contractor business?

I have 4 credit cards started and an SSL set and forget loan with 7 months total of perfect history so far. What else to do?

The mortgage scores want you to have an auto loan but I have no need for or want an auto loan and it's not exactly easy cheap or simple to get an auto loan just for the sake of having an auto loan..  

Maybe I could refi cash out like $1,000 or so off of one of my cars and pay it back? 

Sounds like a silly thing to do but so does a secured loan or secured credit card but you have to play their game.. 

I just want to do everything I can while I can..