by the looks of things and reviews, it's an amazing bike. Yz250f was "bike of the year" last year, and the new "x" is just a close version of that but more offroad friendly.
Two different 'X's in the Yamaha lineup, the YZ250FX, a woodsy version of the YZ250F you're thinking of, and the YZ250X, a woodsy version of the two stroke that Yamaha has been cranky out for years.
If it were me I would look for a steel frame offroad bike. KTM, Husky, Etc. I have ridden the Japanese aluminum frame bikes offroad and they pale in comparison to a steel frame bike offroad. Aluminum is too rigid.
I know the consensus is two-stroke, but I'd ride a 450 in the woods without thinking twice. Yes, they're heavy, but the torque is nice. You can just lug it around and not have to worry as much about gearing or abusing the clutch. I mostly ride moto, but I hit the woods a few times this year and had a blast. I ride a SXF 450 with motocross suspension, and despite being way too stiff, I got around okay.
The YZ250FX sounds like the right package. My YZ426F isn't bad as an other-than-MX bike but it does need a proper "woods" suspension. I went +1 in the rear which helps a bit in tight stuff. Folks here in the East have discovered that Trials tires are a great application, vs knobbies, for trail riding. Would like a headlight. Hell, would like motard wheels and a complete street kit, too.
I'm going to start on done really easy stuff, never had a dirt bike before. Gear I'd adding up damn quick!
Whatever you do, do not try to "save money" on gear unless you feel like putting your orthopedic surgeons kids thru college... If there ever was a reason for all the gear all the time it is dirty bikes...
In 2005 I bought a new CRF250X and still have it 10 years later with no issues. It was the only dirt bike I liked enough to keep for a long period of time. I sent the suspension to Factory Connection, and added a steering damper, and it was money well spent. I also have a set of SM wheels. I don't put many hours on it, some years with zero hours. I've checked valve clearances a few times over the years and have yet had to adjust anything. I also don't rev the snot out of it. Maybe I'm just lucky with mine. I find riding a small bike in the woods more fun than a big bike, but that is probably due to my limited skills. And I've had CRF450s, KTM 525's and even a CR500. The only place I really enjoyed the big CR500 was in huge open sand pits. For everything else, it just brutalized you for a day of riding.
I'm excited to ride on trails, too bad I'm traveling or wife is next 3 weeks then most of December as well.
I have a set of Asterisk Cell knee braces that I credit saving me from injury multiple times. Knee protection is money well spent.
I'm a noob to dirtbikes too, at 45. Bought a pair of KDX 200's. I did a complete refresh on the '03. All new suspension bearings, swingarm bearings, wheel, bearings, new top end and cylinder, new tires, chain, silencer, V-force reeds...It has revalved/sprung KX 250 forks and reworked/sprung rear shock. Havent rode it much, but it is regarded as one, (if not the best), of the all time greatest trailbikes. KTM 200 was up top too. I've about $1500 invested in it. I bought alot of gear too. Gaerne G-React boots, AXO air cage armored jacket, and knee/shin guards. That armored jacket makes a huge difference in confidence and safety. I fall a dozen times each time I ride. Nasty, rocky uphills, flippin' the bike over type of wrecks. The jacket isn't cumbersome or bulky like you might expect. Doesn't restrict movement or anystuff. Some over the boot pants are nice too. Semi waterproff, pockets, padded. Keep you relatively dry and clean-ish.
I'm debating on jacket vs protector and individual pieces. Gets hot here in ga, new to dirtbike as well at 40.