I have experience using DSCR loans that calculate the STR revenue to purchase smaller single family homes.

I calculated a $30k profit. 

you have to calculate the interest costs.and.... it makes zero sense whatsoever to buy something turnkey with that much leverage. none. you'll never, ever pay back the HELOC with the non-existent 'cash flow' from the property.just trying to be realistic. the market is unforgiving right now.

Deduct NEW property taxes after you buyDeduct home insurance costsDeduct maintenance percentage, typically 10%Deduct vacancy+tenant nonperformance percentage(we recommend 5% for Class A, 10% Class B, 20% Class C, good luck with Class D)Deduct whatever dollar/percentage of cashflow you wantNow, what you have left over is the amount for debt service.Enter it into a mortgage calculator, with current interest rate for an investment property, to determine your maximum mortgage amount.Divide the mortgage amount by either 75% or 80%, depending on the required down payment percentage - this is your tentative price to offer.If the property needs repairs, you'll want to deduct 110%-120% of the estimated repairs from this amount.Be sure to also research the ARV and make sure it's 10-20% higher than your tentative purchase price.As long as the ARV checks out, this is the purchase price to offer.It is probably significantly below the asking price.

I often use this to help calculate some quick math on deals.

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

In regards to the numbers you're calculating they seem to be relatively conservative in my opinion, to be direct it's more than I use for homes that are in good condition.

Be very careful when it comes to vacation homes you need to be very experienced to be able to calculate the exact net cash flow. there is so many expenses that you might not understand, in other words you need to do your homework before touching any vacation rentals especially with the pandemic .

Obviously not really big deal if he owns it out right, but it will be something you want to consider in your calculations. 

Quote from @Isuf Aruci: i live in the NY area and would love to build a house or a mid apartment building. but the land search is very very difficult. also lets say i found the land, where would i get information and see if its buildable, also how do you calculate a land to see if its worth building or not.