I played guitar too.
Don't worry too much about planting your two fingers. You need to keep down one so you have a reference point. Eventually, you will feel comfortable enough with you right hand (this took me about a year) that you can just decide if you want to plant one or two fingers and it won't be that difficult to do but for now just plant as you are able.
FMB was the third song I tried to learn. I can't say it was a bad decision but I am glad that I moved on to other songs before I could completely play it. I played that song every day. It started to come around near the 18 month point and at three years I could more or less play it. So it is a long haul.
If you want an easier Intermediate song, try The Old Home Place and then move on from there. A nice beginner tune is Worried Man Blues. And Cripple Creek is an easy one you can impress your friends with.
In my experience you have to learn just about all of the Intermediate songs in order to pick up the basics of the banjo vocabulary that you will need to play the instrument.
Again, in my experience, it's not just a question of learning how to finger the chords and pick and then take it from there like a guitar. There is a definite 'book' of finger patterns you need to assimilate (so they become automatic) in order to play this instrument. The songs are fun way to do this.