Hi @Helena Wu,
I'd say you would usually want a manager that services the area of your rental, since they will have to deal with maintenance, lease agreements, and misc. tasks. Either way they would have to have someone local. There is benefit of having your properties under one management group such as possible lowered costs and good management (assuming you have or find a good group).
You would have options to FHA, 203k (renovation loan), and conventional lending for home occupiers can be down 5% downpayment. Depending on the state they may also have some programs such as first time home buyers, but you can find that out by talking to a lender that services the area you intend to buy. FHA will have some restrictions depending on what your plan is, (e.g. usually you are unable to airbnb in an FHA property, at least for a year or so) However, you can rent out the rooms to tenants.
Some key figures would be to calculate your cash on cash return on investment (CoCROI) and your cashflow. To feed these values you will need the basics of potential rents in the area (can look into current listings, a tool like rentometer, HUD Fair Market Rents, or a local agent), taxes, debt payment for your mortgage, water/sewer, insurance, and assumptions for maintenance, capital expenditure, vacancy, and management fees. Many of these are public information or things you can find by talking to agents, property managers, and lenders.
Older houses are/were built high quality, just different in many cases. There are the exceptions of asbestos and lead paint but that depends on area and can all be addressed. If the visual appeal is the issue those are usually cheaper things to address with paint, molding, and cabinets. Many areas have cheap loans or free loans as options to address the issues of energy efficiency that many homes have like insulation, heating and cooling systems, electrical and paint. This all depends on area, a good agent can help make you aware and don't skip on your home inspection. There are issues with newer homes so I wouldn't necessarily just write off older homes.