I raced a lot of XC races here in Japan back when FS was just coming into vogue. I stuck with my hardtail and with my road fitness base I did alright, (lost a bit of time on the downhills but made up more on the flats and uphills). The appeal of MTB to me was a change of scenery and learning a new skillset. The mental break from road training and racing was almost like a holiday. The atmosphere is generally more relaxed and you tend to hear a lot more laughter on dirt compared to road. Like @bloaker says just having the attitude to get out there and have a go is all you really need. Worry less about your gear until you feel your gear is holding you back. More likely your fitness and handling skills will hold you back more than your shoes. Finally the best advice I can give you is look where you want to go (not the obstacles) and let the bike take care of the terrain. You have ridden BMX and Road so the learning curve won't be terribly steep.