I don't have a "big" steel narrowboat, just a 23 feet GRP (fibreglass) cruiser, and I don't live on it. But I bought it within the last 3 months, and it was my first boat. So I was in the same boat (if you'll pardon the expression) as you. The main problems I had to overcome before being able to go to my boat and step aboard whenever I liked, were to do with finding a boat, buying it, and tying it up where I wanted it to be:
1 - I didn't know anything about boats - just always wanted one, though not to live on. So before taking the plunge, I joined this forum (and another one for the make of GRP boat I had decided on getting) and spent a very long time reading through previous posts. I read everything. This taught me a lot about what I was letting myself in for - costs, pitfalls, legal requirements and so on and on and on. I learned a lot. I think this was the most important preparation for boat ownership that I made.
2 - I didn't have anywhere to keep a boat. This is something you need to think about before you buy. Where is it going to live? Can your hoped-for mooring-place accommodate you? What will you do if it can't? In my case, there were two marinas relatively close to my home, one 35 minutes from home by car, and one 45 minutes away. Both could fit me in. I went for the least costly one, which happened to be the nearest one.
3 - When you find you ideal boat, where is it? My ideal purchase happened to be 55 miles by road from where I wanted to keep it, or 65 miles and 104 locks by canal, which would take me between 5 and 6 days. As a beginner, I didn't fancy doing 5 or 6 days, single-handed, on an unfamiliar boat. It cost me several hundred pounds to have the boat craned out of the canal at one end, moved the 55 miles by road and craned back in again at the other end.
Hope this helps.