I created kind of a checklist of things that made the site somewhat successful @ https://news.ycombinator.com/item?id=9837727.
Some personal thoughts if you go down this path. It take a long time to build a following (think 1+ years). Make sure you get RSS feed & email list going from day one (this was a big selling point). I went down the subscription path and was making about $1-2k/month (at $14/month). That was after spending a year putting in 60 hour weeks. Transcripts and diagrams came in really handy in driving traffic to the site. Google was really helpful in building a following. Not saying it cannot be done just that you need to really love what you're doing (in that you'll want to give up before you see a return). Do not skimp on production quality. Having highly edited content with premium audio makes these worth watching (that's the differentiator from other content). Just watch railscasts.com and you will instantly see that quality vs some random youtube videos.
Burnout can also be a real thing here. You paint yourself into somewhat of a corning, in that you are charging a monthly free, for something that requires creative juices. I found there to be real pressure to produce new and exciting content, but what if it is not polished enough or up to your production quality control bar? Might be a good idea to have somewhat of a backlog so that you fall back on in the event you have writers block. I had a few episode, where I just could not write for a couple weeks, or the content was just not up to my production standards yet. You'll also find that as you progress into writing something, you'll think of a much better way to tell the story, then you'll want to re-write on a tight timeline. It was brutal having to produce on a timeline like that.