Depending on your practice size and income level, you may just want to start with maxing out 401k and also adopting a defined benefit plan before committing to becoming a lifelong real estate investor.  

You'll get differing amounts and qualities of leads depending on the type of marketing, but also depending on who you're marketing to and where.

When I was in your exact situation looking for help, they were the only ones that provided solid answers and walked my wife and I through the full transaction.

It would depend on your income, location and price of the home. 

If they are the one providing most of the cash, they might not want to carry that liability, but you've already negotiated with your partners on this and then the bank isn't cool with it, you could be in a pickle.

Not sure you really make more money.BRRRR would be interesting if you can find it.Flipping is competitive and brings in cash but not long term wealth.They all are great options, it just depends.

Sometimes they forget to tell you that many tenants in Detroit don't pay (depending on the property manager skill and the type of tenant) - but taxes are very high in the city and so is insurance. 

There are a few specific area we target in Sacramento depending on your goals.

@Arthur Savery there are some great comments already provided.

Make sure you and your mortgage provider understand "delayed financing".