I'm no old-school cinephile, but I've listened to enough of them to understand that if you're really into the nitty gritty details and love soaking in every corner of a filmed image, there is no substitute for a large print screening. But YMMV.

If you are a film student. Yes. For most folks 5 hours is a lot of driving. Film is the way that Christopher Nolan intended but the digital versions exist just so that most people can experience it. Don't feel like you missed out if it's just too much driving. The story is what is key. Not the projection technology.

I've never actually seen anything in 70mm IMAX, so idk! But I love the vibe of analog film and the way it looks, so to experience Nolan in the way he intended it at essentially 16k resolution is likely going to be incredible. Five hours is quite a lot though, especially to then watch a three hour movie. Maybe if you made a weekend out of it and stayed at a hotel or camped somewhere? I'm lucky that the closest one to me is only a 45 minute drive