Our only option would be a portable one but I’m wondering if it’s worth the investment?

Here’s the month one progress: So far upstairs hardwood has been refinished, master closet has been gutted, plumbing has all been replaced, loft space is closed in, upstairs windows have been replaced, popcorn ceilings have been scraped, drywall upstairs has all been taped, finished skim coating the walls upstairs, and yard has been cleaned up.

You should only have it running when someone is there and/or use portable heaters for heating quickly and directly where the work is being done.Also, may want to consider looking for a leak somewhere if making those changes doesn't move your bill down.

Currently, the central room can potentially be converted into a room (it has closet inside there, the room only needs a door).

I’ve tried and failed at a number of different business ventures (got a closet full of fidget spinners I couldn’t sell as a reminder).

There are far too many things to list so I won't even bother.Be sure to look in every unit, every closet, every appliance, every window and screen, floor and ceiling, etc.

It works on cell signal, easily portable to the next project, and fairly inexpensive.

I am looking at an electric water heater, closet heater, first floor.I only owned this place for a month now and I'm trying to save while I build reserves. 

The house is about 4600 sq ft and it has 6 bedrooms (7 if you add a stand alone closet from IKEA in the office).

I probably tighten, lubricate, replace or repair over one hundred small things from toilet flappers to closet doors when a unit turns over...it is far easier than doing each one when they break, which means we have to schedule an individual call for each one, move all their stuff out of the way, fix it etc...in fact, if I do get a call, actually not that common but does happen, I make sure and say "what else" to get it at the same time....so just trying to consolidate more maintence, especially when you have full access to the unit, may help.