I went to sign up this morning, and it costs an additional $100. 

Is there any good rules of thumb to estimating the cost of a boiler?

While under contract, we perform due diligence and there will be some soft costs incurred. 

However, our tenant turned out to be problematic—late payments, issues that led to an eviction, and additional repair costs before we could relist the property for sale.Now, after months of making mortgage payments out of pocket, we finally have an offer.

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

If you have a good FICO, a decent down payment and closing costs, go ahead an do the first one. 

It costs money to own and operate real estate which is why you need a primary source of income. 

Refinancing has more nuances than it seems, and so do closing costs.

I have not looked into this but, if process ramps up, could cut construction costs, time to market and massively increase supply, too. 

Those situations go bad more often than not, costing you money and the friendship.