In looking at properties, storage units seem like a great investment.

You own a rental unit, not a free storage unit.Just make sure that you document all communications with the tenants.

Then I had her set up a new one for a self-storage business

They can use it however the need to.We took down the names of the people making their home in the commune in the woods and got their shoe sizes.

Yes, they're nice to have, and I am sure they have their perks, but to me it seems like more of an aesthetic preference - one that generally isn't a deal-breaker.Or you could view it as an insurance investment.Now, if I had a tenant who happened to be a carpenter and who wanted to build a storage shed in his yard, I would offer to pay for the supplies because I could market that to future tenants and hike up the rent. 

You could likely get a variance, but even then would be be shoe horning a house between the other two. 

Possibly think about renting it out as storage/ install some coin operated laundry machines.

There's potential to add paid laundry or extra storage facilities in the unfinished basement - which might increase your returns a bit.

I thought that due to the rise in e-commerce, we could buy these spaces and convert them into "last mile" storage facilities for online retailers.

given the current situation - Self storage (couple options) - Dialysis centers (couple sets of dialysis centers)I would estimate that this half of the investment would generate a 8-11% IRR long term.