My wife has an old 401k rollover from a prior job that we're both interested in rolling into a self directed IRA and investing in RE projects. 

Doing so may give you an equity position in your current property that you can use to roll over into the purchase of another property. 

Also, if you have tenants in place, you'll have to wait until your leases roll over to implement this charge; however, I would think you'd have to do the same if you sub-metered and wanted them to start paying for their own water.

I have roughly $100K in a rollover 401k from a previous employer and I was thinking I could put that in a self-directed IRA to put a sizeable down payment on something that I could personally live in.

Look into doing a rollover to either a self directed IRA or a ROBS 401k (Roll Over Business Startup), perhaps you delay the taxable distribution.Good luck.Carol

I do know unfortunately that I can NOT roll over funds ALREADY in a ROTH :-(.

Do you bill the client (me), or do you allow for rollover if you continue to be engaged for the service until consummation?

You would need to open a self-directed IRA and then transfer or rollover you existing retirement funds to the new SDIRA.

If I do need to include that money, I've got $170k in value I need to roll over. 

When your did the rollover from Fidelity into Solo 401k, Fidelity would issue 1099 form also, but that is completely separate event.