Choking kink + anal help

So i’m into choking and my bf and I are a young couple. I have told him I want to try it and I said if he doesn’t want to it’s cool I understand it can be a scary thing. He said he’s up for it but wants to do it in a safe way and I’m not sure if he wants safe words or something etc and I’m having a hard time communicating what I want to him. We haven’t actually had sex but we’ve done a lot outside of dick in vag stuff and he recently confessed he really wants to do anal and so the other day we tried it but his dick didn’t fit and things got really awkward really fast and I told him he would have to finger me so it would work, so he did but it still didn’t work and he started getting soft and we just ended things awkwardly but he texted me and says he wants to try again and this time he’ll bring lube and stuff but I’m really nervous that it’s going to hurt bc just his fingers hurt

This is all very tmi and yikes but pls help