He will pay sales commission but get his BHA back and have lived for rent free. 

what would be the justification for paying that much?

Imagine making millions of dollars over the course of your career and then having to pay 30-50% every year to uncle sam instead of compounding that cash over time.This is exactly what real estate professionals have learned to mitigate.To reduce their taxable income, they just buy a building every year, do a cost seg, and use depreciation to reduce their tax liability dramatically.Their personal wealth snowball grows much larger and much faster than their W2 counterparts who give most of their money back to the government each year.Following this strategy as a real estate professional is one of best ways to end up with a much larger net worth at the end of your career.

I'm thinking if I ask the tenant to pay the other half, I'll probably need to make an amendment to the lease to reflect that.

@Cole Starin sometimes it makes sense to sell the WORST property in your portfolio.Another option is why do a LOC on the duplex, when you could just do a $100k cashout refi to pay off all your debt AND keep the property?

Your first year will be a learning experience, you will want to be close to the action, as you may not have the capital to pay someone to handle everything.

The hang up is getting deals formally drawn up.One idea:- I buy the property and pay 25% DP, then they provide capital after the closing and I pay them P&I over 5-10 years.

That's basically what I used propstream for the most and if I can pay 100 a month for resimpli and get those features and also the crm and accounting features I'd be happy. 

How do you pay for the tax and insurance?

Billing is different for most and more than likely, you'll pay a retainer of some sort up front and have a balance due.