Has anyone converted one of these to efficiency rentals?

Cons: This doesn't seem like an efficient way to scale the business and eventually, I will either have to quit my full time job or find a property manager.

It depends on your climate, you might do an energy audit or just switch to electric, it doesn't seem too out of line for four units though $35 ish dollars per month depending on the size of the unit and how much they use the climate control.

We are both hard workers/high energy (not necessarily incredibly handy) and wouldn't mind doing the lion's share of the work by ourselves.

Until then, nobody can help you and all these posts are a waste of time and energy.

In other words, if you desire a 10% cap rate for an asset it may or may not be relevant because if the general market is willing to purchase at a 6% cap rate you will be outbid (assuming the market is efficient). 

I've done most of the work on all the properties myself, but am now trying to move away from that since my job has become much more demanding and my time much more limited.I'm looking forward to contributing to the forums where I can, although I'll be the first to admit that the way I've done things in the past probably haven't been the most efficient way to go about investing.

I don't have the time or energy to do this myself this time around, so figure it would cost me $20k to have someone do it for me. 

This is true for all aspects of REI, either DIY and risk a mistake, or pay someone else to do it more efficiently.

Go ahead, efficiency is the way of the future and they will save you good money.