I have a large cash infusion (selling a building) coming in 10 years. It then becomes
an investment (cash). How do I set this up to show income off this investment starting in 10 years?
If you click on Cash Infusions and enter the net value of the building... you can set a growth rate if building is increasing in value... Set the Start Age to be your age in 10 years. Set Duration to 1. If you set last column to Taxable, then the money gets poured into the Taxable bucket and will grow at the aggregate rate of the Taxable investments (as shown on the front screen).
That is the natural way to do it.
If you say "Yes but I just want to model the income off the investment and not dip into the value", then you would need an estimate of that income. If you want to do that, then don't inject the net value of the sale as a cash infusion at all, but simply enter the income from that investment as a Cash Infusion.