So I can buy a rental lot, but I can't do anything with it. How do I buy a lot build a house on it and rent it out to people for money?

Hi there. It's possible I am not understanding the question entirely. Your sim owns a second lot as a rental property -- with testingcheatsenabled True, can you not shift-click on the ground of the lot and build a house there, with the costs of building being charged to your active household?

My experiences with this feature on the landlord side have been limited to my sims purchasing lots that already have homes on them and with tenants already in mind, so there might be a barrier to what you want to accomplish that I haven't seen yet.

I was hoping I could buy this culdesac of lots in sunset and own the block and rent it out. I didn't think of using the testingcheatsenabled to build, how do I get tenants?

Once you have a rental property that sims would actually want to live on and that, if you have the criteria enabled, passes household inspections, then it would be a matter of waiting and hoping for some sims to move in. At the very least, the new lot must have a fridge. For most of the other criteria, NRaas > SP > General Options > Options:Lots > Options:Inspection

If you have SP Immigration going to any extent, incoming households should consider your rental lot(s) alongside of any others they may choose to move into.

For a less random, more player-controlled way, you could force sims already in your world to live there as their own household by using MasterController's Add Sim command on the lot.
 

I don't see the options:inspection option

Do you have SP's progression enabled? If not, the options it cannot use get hidden.
NRaas > SP > General Options > Enable Progression > True

If it's not that, it is possible that the Inspection options require one of the SP modules such as SP Extra (the others like Career, Skill, Relationship, Population do not seem relevant in this case and we know you already have SP Money), but our documentation does not indicate that.