Their kids have written on the walls with crayons, the vanity installed 5 years ago has been scratched to the point it needs to be repainted (it is white and a lot of paint has been scratched off), the caulking around the sink and tile has turned black, the hardwood floors are extremely dirty and will likely need to be sanded and stained and the carpet must be replaced. 

I wonder if it's cost-effective and even possible to install those in duplexes in Phila.

A lot of people paint the stock tank or create a deck around it to make it look really nice.First, it's cheaper and easier to install than a pool or hot tub (can do it in a weekend).

They said that i have to have the plumber come and bring the house up to code and install a handgate valve. 

Also, with two separate meters I would think that the utility company would need some documentation from the city before installing that.

Then, I go in and install all of the utilities and road while I am building the duplex.

Installing tile is easy, but takes time to do a good job.

A curved shower rod is $30 and a crappy on is $10.These are the type of things that can matter to a tenant,  but round off to $0 when I do my math.Permanently installed shower rods (screws rather than spring tension) last longer and don't scuff up the wall as much.  

These cracks look deep and not something that can be fixed with cement.As a side note, it looks like there is likely leaks in between where the slab and wall meet so on top of doing significant foundation repair, you'll need to install an interior or exterior french drain.I am only going off 3 pictures so I could be wrong but this does not look like a cheap and easy issue to fix.

Therefor, I don't think you can give any general ranges for any of these items.It also depends on the quality of the item that was installed in the first place...and who did the installation.On top of that, items like furnaces, which demand maintenance (changing filters regularly) will have a shorter "shelf life" in rentals since tenants are notorious for not maintaining them.