Welcome Peter.
A caveat: I'm new to this myself having just bought my first property in Philadelphia. I'm a New Yorker and moved here a month ago, but I feel I got to know some areas pretty well through my house search. I was also considering just being a passive out of state investor.
As to the question of where to buy, I second the endorsement for South Philly close to Broad. The deals are better on the west side but the neighborhoods are more of a mixed bag. Very much a block by block situation as described above. I'm bullish on this area mostly because I think it's such a great neighborhood myself, and just expect people to realize that as prices push them farther south. That said, I'm a little daunted by the successive, seemingly eternal 'For rent' signs on some of my neighbors houses.
I think Port Richmond is another good spot for buy and hold investing. The property value won't appreciate as fast as some other areas, but the buy in prices are reasonable and it's a pretty safe, stable area. It's less block by block than South Philly. The area from Aramingo to the river is safe. I haven't made an exhaustive study, but I think you could get solid returns there and its adjacent to Fishtown, where people are getting priced out.
For speculative buying, Brewerytown seems like a good bet especially if you find a deal along Girard Ave.
As to investing remotely, all the cities you mentioned have plentiful offerings through turnkey companies. The site Hipster Investments aggregates deals from different companies. They like Chicago a lot, but feature several offerings in Philly and Indianapolis. The prices seem competitive and you don't have to worry as much about the quality of the neighborhood because when you buy from a turnkey company you also buy a management company.
To get a feel for an area without visiting it, I find the maps on Trulia really useful regarding crime, commuting times and area businesses.
I'm probably way to new to this to be offering this much advice and welcome corrections from more seasoned investors.