Joe, I agree with everyone above.
Good on you for putting on a longer seatpost. But PLEASE be sure to pay attention to the seatpost's marking for MINIMUM INSERTION. you need to have sufficient seatpost inside the frame to prevent excess stress at the frame juntion of top tube, seat tube, seat stays. if you didn't notice the marking on the seatpost, loosen it again, pull it out, and note where it is marked. even the cheapest Taiwanese posts will have some sort of marking for minimum insertion.
second is to adjust the saddle tilt and fore/aft. if you tilt the saddle with too much "nose down" (the tip or nose is pointed toward the ground) you will quickly tire your hands and shoulders, as you have directed more weight away from your butt/saddle point and to your hands/handlebar point.
conversely, too much "nose up" will remove weight from your hands/handlebar and put it on the butt/saddle points, which might make your off-the-bike sit-downs for the next few days pretty painful, even on the most comfy sofa.
the uglier part is that for us men, too much "nose up" puts a LOT of pressure on the prostate and can lead to "sleepy peepee" in milder cases and tissue damage in worse ones.
saddle fore/aft is just the act of sliding the saddle on its rails within the seatpost clamp. you want to approximately put your knee's foremost point (the kneecap) plumb over the ball of your foot when your foot is at the bottom part of the pedal stroke. move the saddle fore or aft until you get near that point, and then make microadjustments as needed to stay comfortable and/or deliver better power.
tire pressures should be about 35-45 psi, check the tire sidewall for range.
make sure the brakes work well and slow you down sufficiently. get used to their power before taking the bike down any serious descents.
make sure the gears shift smoothly from one to another. if they don't, you have to decide whether to become an amateur wrench or to give your local bike shop some business.
you can always PM me if you have weird/random Qs too.
good luck and welcome to the sanest group of recreaters on earth. we are better than skiers, if I dare say. skiing tries to be as good as MTB riding. it comes pretty close some times. usually when there's snow on the ground, if you catch my drift.