When do I become a resident of PA? Is is automatically applied once I move there and start working there? Or is there something more official I need to do i.e. file paperwork with some government agency? Once again I highly recommend you seek a local professional to discuss all your questions. Check with PA for the residency requirements. Usually when you move you need to change your DL, voter's registration, etc. which will set up residency status.
How do I give up the homestead on my NY residence once I convert it to a renal property? This is done thru the RE tax office.
What if I decide to keep NYC as my primary resident, rent an apartment in Philadelphia while working in Philadelphia? Will I end up paying more in taxes? Again this is a longer discussion you should have with a local tax pro since what is legal and what you can do and how it affects your tax situation is too intricate to be addressed in this public interntet forum. One item you will need to address is the renting of your personal residence ... need to let the state/city/home owner's insurance/mortgage company know of the change in use just to name a few subjects to discuss.
