For point 2 yes the homes are much older. You'd be hard pressed finding a rental built after 1910. But all of that can be eliviatred on the original rehab. Just make sure you take care of all outdated items and you won't have a problem.
Point 3 umm it litterally changes by the block so that's tough to say. Some great areas are Trolley, Triangle. and Cool Springs. For "Okay" I would say Little Italy, Baynard Village, Brandywine Village are fine. Everywhere else you're gonna find it hard to justify the purchase if you're banking on appreciation and not pure cash flow. I mean granted this market is nuts right now and typically some areas that wouldn't sell for much are flying off the shelf but in general I'd lean towards those areas.
"Downtown" has two main distinctions Market St and The Riverfront. Those areas are pretty much all changed and the Riverfront is building new things by the day.
Would love for someone else to chime in with their experience as well.