want to understand rental cashflow analysis better

[Gentle LeBrane]

Good morning all, i have been learning numbers and im finally understanding a possible good deal. Would like some insight as to if im correct or on to a good start with where i am at. Thanks in advance! 

Mock example deal: 

Asking price:20k, ARV 100K, Rehab 20k (my question is here too), rent income 780.00, desired cashflow 150.00(looking at the asking price as though it were a 5 unit multifamily-so counting rent for 1 door)

Rent 780 minus: cashflow 150.00, proptery mgmt @ 10% 78.00, maintenance @ 5% 39.00, vacancy factor @8% 62.4, collections mrkt@10% 78.00 total max pymt 372.6 minus:

Im guessing home insurance @ 54.17 / month and taxes @ 67.5/month (of course guesstimate for learning sake)total to max pymt of 250.93 i then take this number and figure the loan amt into my loan calc at rate of 4% (bc i have seen some lenders advertise 3,4,5% loans) came up with loan amt of 52,560.11 then subtract rehab of 2k and closing of 2k and have max offer of 48,560.11

Now i understand the math better since i researched a walkthru. However, i would like some advice on if im looking at it right bc im getting ready and an more comfortable with seeking a loan to nab my first acquistion and am excited but i want to be sure im understanding the numbers correctly and thoroughly. So in my opinion i believe this deal has some good skin and would be profitable. What does one with hands on experience think? And abt the Rehab price in beginning and end. My question is if i did my max offer at the 48 then what was the 20k for in rehab at beginning? I understood the rehab figure at end. But. Was lost at the figure at beginning. Like is that figure that the seller did or the rehab i have to do? Im looking at it like whn the math is done and u subtract the max offer from closing and rehab cost thats it ..im not seeing why the 20k would be there. Again thank you all for any and all clarity. Im really anxious to start but i dont want to be ignorant. 

-Gen