I would think -- and this comes from someone with zero experience in law OR apartment buildings, that the sale of the property would be outlined in the existing leases, as well as the options thereafter for the new lease-holder; and this would be trumped by landlord/tenant state law.Given it is such a large purchase and you could potentially be disrupting what is a relatively stable situation, I would consult with a lawyer to determine your options.

If the listing broker gave you the code then the seller didn't give permission but their representative did so any problems would fall on the broker/agent who did not follow the protocols outlined in rules and regulations and the listing contract signed by broker/ agent and the seller.No way ever I would go into a property without permission.No legal advice.

A rough outline for a standard operating procedure can be found here.For more complex tasks, I've found screen casts to be very helpful.

I echo pretty much everything he outlined.

I'm sure there are existing forums outlining what to look for but I'm on the app right now and was going for help outlining how I should run the numbers or links to threads that do so.

At that time, I'll have to look to larger and larger projects to meet those two criteria I outlined above.ROI is important, but only in the context of meaningful investments. 

The CG is not on the lump sum of the sale, but (ignoring lots of details) CG is (Net Proceeds of the sale) Less the (closing costs of the purchase) times a CG tax rate.There's lots of adjustments but that's the outline.

Basically what I'm saying is that sure, those very specific scenarios that you outlined are unlikely to happen again, but really what's important are: land limitations and demand.

It does not matter if it is effectively the same (even though it isn't, for reasons I've outlined above).

If it was me I'd probably start by considering holding the property in an LLC and outlining everyone's ownership interests/contributions in supporting documents and including procedures for disagreements, buyouts, etc.