I didn't read all 9 pages of responses so my apologies if this has already been covered. Also didn't see where you were located. When we bought our place it was almost the exact scenario you describe and here's what I would say:
Building a gravel road: We've gone down that road (no pun intended) a couple times and the answer is real easy: hire that out. I wouldn't touch that with a 100 foot pole. No way no how. Never. You want no part of building 1500-3000 feet of gravel road yourself, especially if all you have is a tractor - don't care how big it is. However, you can maintain 1500-3000 ft of gravel road easily with any compact.
Timber and trails, light grading and gardening: Been there too. Cabs are terrible in the woods and so is a tractor that's too big. This stuff is all pretty easy, any compact open tractor will do great and is usually better.
Mowing: Don't mow with a tractor if there's any way you can possibly avoid it. Seriously. If your pasture is big just lease it out for hay. If it's small (5 acres or less) get a ZTR. You'll question that logic when you have to write a check for a $10,000 lawn mower but a year later you'll view it as some of the best money you spent.
As for the rest, smaller tractors aren't "learners", they're just appropriately sized tools for the jobs they're doing. Some feel bigger and heavier is always better but keep in mind:
- If you plan on trailering it anywhere for any reason, smaller and lighter is easier, cheaper, and I'd argue safer. And trust me, you'll want to trailer it somewhere. You get an M4 with a loader and a trailer to hold it, you're probably over 10,000 pounds which is more than some standard F150s are rated.
- Bigger and heavier means it's not as maneuverable or nimble in tight places like woods and trails.
- Bigger and heavier is usually more expensive to buy and will cost you more to use.
- Bigger and heavier will tear up your yard just by driving across it. May not sound like a big deal but I promise, it's a big deal.
- Bigger and heavier is harder to store, assuming you don't plan on leaving it sitting in the yard and don't have a proper building you can use.
You'll end up doing many other things that you haven't even thought of, and that's the great thing about having a tractor, but with all that said you probably already know where I'm going. Honestly something like a 3 series Deere is all you'd need.
I sometimes dream of getting a big tractor with a cab and all that other big tractor stuff just because they're cool and I love tractors. I may go there some day, but if I do it won't be because it's a better tool for the jobs I have on a place that sounds just like yours.