These are great questions. When you purhcase a tenant-occupied apartment you are considered to be an investor which may affect the type of loan you can obtain. You should check into this first. In Westchester rent regulations are based on ETPA; the Emergency Tenant Protection Act. It has many similariites with NYC Rent Stabilization and Rent Control. If the tenant is a Senior Citizen under Rent Control, they may also be be subject to SCRIE (senior citizen rent increae exemption), Their rent can be increased only very little.
The big issue for you is that the tenant can stay there for as long as they want; you have to offer a renewal lease in accordance with the increases allowed by the rent board. If the apartment is inexpensive enough, the future resale potential may cover the monthly shortfall. Keep in mind you may be waiting a decade or more.
You also need to ask why ae the circumstances of the sale. Is the sponsor selling? Are their sponsor rights associated with the apartment? Most buildings today will resisit a sale with sponsor rights but you should check.
Sunnybrook is a nice property with better than average parking and you can walk to the village. The walkup nature of the buidlngs is a bit of a detraction, and it is common knowledge that the Met Life buidlng across the street may be redeveloped. This may be a non issue depending on where your apartment is located.
Any other questions please email me through my website!