Would this be a sufficient size to add another 1bed/1bath apartment to?

Also decent sized deals for larger fees!

There is no "one size fits all" answer here. 

i guess that depends on the size of the deal.As far as flipping goes,  how is flipping any different from buying a stock and selling it for profit?

I think when you hire a PM you have 3 choices 1)  A very small local provider (<15 units) and they tend to me 1-2 person operations, they are the one unclogging toilets, answering guests, etc and it is tough to do everything, so things lack. 2) A large/nationwide provider where you are only a number and they usually lack local resources 3) A mid size local provider who have resources and you are not just a number.Through effective revenue management with a revenue manager, and being listed on 15+ sites including Marriott Homes & Villas, JetBlue and Allegiant Airlines, Hyatt and Amex Travel (coming soon) we are bringing in more revenue than most can self managing, offsetting our fee.One of the top questions I tell people to ask their manager is the fees, who keeps them? 

Those algorithms compare homes based on general location, size, # of beds/baths, age, etc.

There's no one size fits all answer to this question.

If the price to replace is within budget I'd do it because you're putting out a newer/safer/more reliable product.2) Cost to replace the entire systems is tough to gauge without knowing the building size and style...

Moreover, there are leasing companies such as PadSplit and HomeRoom who implement this daily, but for your property size/scale, I don't believe they'll be necessary. 

All of that being said, most property management companies of any size likely have full-time or part-time handymen (for lack of a better word) that that service simple repairs across units for multiple owners.