First off, welcome! Does your friend who is rehoming him have kids or has he been around any that you know of? Are there behavioral issues as to why they are rehoming or is it financial or what? Generally bullies tend to love kids BUT not knowing the background of this one there is no way to say. 2 1/2 is a tough age if this pup hasnt been socialized around them so I would def be extremely cautious as you get to know him and keep him separated unless completely supervised. We almost took in a bully many years back that was loving and in need of lots of spoiling to say the least BUT as soon as we brought him in we saw that he wanted to bite at my daughter. We couldnt wait for that to happen so we found him a home with someone who did not have kids. How wonderful that you are willing to take in this baby and give him the love that he should have had all these years. Bullies are not outdoor pups. As for the transitioning indoors, you will get much help here. I honestly dont have much advice but what worked for us with all our potty training was treats treats treats. Everytime they potty outside, give a treat and they learn FAST what to do to get another.