Any Simple Calculation to sell current SFR and buy Duplex?

[Naomi Reed]

Are there any calculators out there - at least to get an idea for the below? 

What if he sells his primary mortgage residence SFR (He moved out 2yrs ago due to a job, and it's been vacant doing nothing! I suppose he can still get 250K tax exempt for capital gain as a single man), and buy a duplex or triplex instead? What do the numbers look like? Is there any simple calculator where you can put a few simple numbers to give him an idea of the outcome after 5 yrs, 10yrs, etc? Something that can incorporate Net proceeds from the sale, tax exemption, purchase price of new property, property management fees 10%, new property taxes, maintenance fees, etc etc.

I understand that it will involve so many details to get the exact numbers - and I do appreciate any input you can give me for that matter - where to start.

Thank you so much for any advice you can send me!