Ride with people faster than you.
Get a road bike, ride it.
Always ride for fun, as in NOT on the spin bike.
yes-yes-and yes
ride yer bike. no time for plans at your stage of MTBing.....
if you want strength for next year in your legs, the only thing i would suggest for you to do is squats. 8-12 weeks of squats over the winter will be a nice arrow in your riding quiver next year.
other than that - RIDE YOUR BIKE FOR FUN.
training is a job - you already have one of those.
ask the riding experience and age of those suggesting you to train with structure v/s those suggesting to ride your bike as much as you can.......... with [relative] age comes wisdom. the exception to my general age comment is MK - he learned quickly and after only 2(ish) years on the bike is stupid fast.
once you have that "nod" from the riding community that you are "there" - then add structure. you will know when you get there.... the force will be with you.