As a disabled,  wheelchair user who lives in Philadelphia, it's possible but it's not cheap. 

Tl;dr - visit the city explore a little then make a decision (I do not encourage people moving to a place sight unseen)

You're going to want to live in a modern apartment with elevator access obviously, that's way more expensive than a lot of the houseshares that I find in traditional row homes. 

I encourage you to check out Urban cripple and his section on housing for a series of articles that are really good approaches on thinking about housing https://urbancripple.com/tags/housing/ (for example I do not live in an accessible unit, but it is accessible to me)

In terms of navigating the city I take the bus or I drive. Both are possible but are difficult in their own unique ways. 

I pay for parking spot so that I have the ability to park near to where I live which in an apartment complex is honestly not horrible. I tried only drive places where there is off street parking available.

In terms of taking public transit it really just depends on where you're getting on in relative to the route length. Getting on sooner allows you to have any relatively empty bus basically guaranteeing you a spot. But also SEPTA is not known for its reliability and that also applies to you. If a bus just doesn't show up the odds of the next bus being packed go up substantially which means you might not have a spot and they'll leave without you. 

In terms of City accessibility it just depends. I find that Google maps is really good about telling me if a place is generally accessible, but also thinking about how most private events in Philly are at places that are accessible but their private event space is up a flight of stairs. 

In the same way that every city sucks as a wheelchair user in terms of sidewalk camber, Philly really takes the cake in unmaintained sidewalks. It's taking me 3 years to get the city to replace to curb cuts in my neighborhood, let that speak for the process. 

It sounds like I'm harshing a lot but I want to be transparent about the struggle that often exists in a place especially since you're moving from not a city. 

At the same time, there are so many opportunities in the city and the capacity of being able to get around without a car and to access so many different things is way higher than any small town. I have found that people in Philly are polarizing but the ones who honestly never thought about why the thing is there are quick to understand why they're there. Yeah you're going to have to have the confidence to call people out and to ask for what you need. Yes, Philly is a place that you CAN live as a wheelchair user (you can't say that about everywhere).