I currently have 5 mortgages but have not been great at keeping track of the details such as costs associated with each individual property.

But you will increase costs in regards to insurance or lending..You still risk losing the property to any liability that happens at the property or in your personal life.

For example,Late RentInsufficient FundsUtility ReconnectionReissue CheckA/C Clean ViolationPest ControlRenewalMove-Out AdministrationUnlock RequestKey RequestFailure to Return KeyPilot LightingGrilling ViolationGarbage ViolationClogged Drain / Tub / ToiletWindow ScreenHurricane Shutter ViolationSmoking ViolationLease Amendment AmendmentPet ApplicationUnauthorized PetGuest ViolationUnauthorized OccupantInspection (due to tenant violation)Yard RemediationPool RemediationSmart Home Device TamperExterior Maintenance ViolationParking ViolationCommunity Amenity ViolationMarketing (tenant early termination)Notice (due to tenant violation) PreparationNotice DeliveryLien ViolationSubleaseAssociation ViolationEviction (not including attorney’s fees and eviction costs)Rent Verification10.

on the bleachers right now just learning so i got a question If I find a  duplex for 350k, put 20% down , 30 year mortgage after the 30 years is over and the property is paid off,  it cost me more than 700k that just doesn't sit right in my stomach.

Has anyone on here done something similar and remember the cost or have an idea of what pricing should be (ballpark)? 

Could be an absolutely gigantic cost and ruin the deal for you, or could be small.

The barrier is the additional complexity - now you are operating two sets of books, and filing two tax returns, and have more operating agreements, more state registrations, etc, need to manage cash better, need to keep in constant mind that your rents need to be a supportable FMV, which may require getting third party certification on your rents so that in the event of an IRS audit, what you have done is supported.In short...the size of the project, and the taxable income, need to be of enough scope to make all the additional costs and annoyances worth it. 

They can’t lend you more because if they have to foreclose it will cost them at least 10%.)Then you want to take that $300k and get a loan for another $300k with that $300k to buy your dream home.

There are some bond programs both county and state level that you can get the downpayment and some closing costs paid or go new construction and do the same via the builder.

@Rania MutumheHouse hacking means turning a place into a rental space, which calls for fix-ups, planning costs, and expert help.