Estimating monthly expense of property BEFORE buying?

[Steve C.]

I want to buy a $150k-$200k mixed use investment property.  The first floor is going to be office space for my practice (Sex Therapist) and the second I want to be an apartment with separate utilities that I can rent out or use for AirBNB.  

I already own a home but it was not occupied prior to moving in.  We did not check to see what water, electric, etc. was each month and just took the prior owners' word for it being "cheap" to heat.  And we really just winged the purchase which wasn't smart.  Came to find out the radiant heat in the ceiling was close to $1k/mo to run and wasn't heating the house well at all.  The water bill is doubled because a separate company owns the pipes and the city provides the water/filtration, etc.

That was close to 10 years ago and, in the beginning we had a few close calls but now we are in a completely different space and doing really well.  

But I know what I currently bring in each month and I want to make sure I can comfortably afford the property prior to purchase.  

How do I figure out with some degree of accuracy, what my monthly expenses will be  for whatever property I buy?   Not just utilities but also factoring in the mortgage, maintenance, etc.

Thanks!