Congratulations Commok, and thank you for your dedication for 31 years of military service. My impression is that you may be way, way overthinking a simple issue. I think your needs are very simple and you might be overspending a bunch of money. Since you have never owned a lawn or garden tractor, and you say your need primarily to mow your lawn with a rear bagger, why not spend some quality time on craigslist and see if you can find a great deal on a good used mower? I don't know where you are located, but in the Dallas, Texas area, good deals are easy to find. I'd first look to see if I could find a good used lawn tractor that will meet your needs. Why spend $10k+ on a lawn tractor if a $2k deal off of craigslist will do the job? If the craigslist deal turns out to be a bust, sell it and move up. At least then you will have a better feel for what you need.
1*I would not see any problem with buying a JD x300 for your small yard either. How may K46s can you buy for the price of moving up to the x500 or x700? My guess is that you will never have an issue with the K46. The x300 has a rear bagger you'll need and may climb your hill without any issues. With the weight of the rear bagger and your substantial weight, you just may be wasting money to get 4wd or a locking differential. You have a small yard with a few challenging spots. If you buy the x300 and turns out to be inadequate, what have you lost? You'll be able to sell it or trade it back in without any great loses.
2*Finally, as LBrown will surely tell you, there are lots and lots of BX-series Kubota tractors out there for very little money. These can all be fitted with turf tires and mid-mount or rear finish mowers, but rear bagging may be harder to find.
I don't think you really need one of these, but if you want one machine to do everything including having a small FEL, then maybe this would be a solution.
3*I just don't think you have the yard and acreage to justify an x500 or x700 lawn tractor that will set you back $10k to $15k.
