If you're going for the 5 year no interest, crunch the numbers and you'll see how much more you'll be hit up monthly. You'll be surprised how little. The dealer will print you out all sorts of comparisons.
Re: Rotary Cutter (brush hog). Get the inline shaft clutch ($210). Kubota PTO drives tend to slam into action vs. controlled spin up like the JDs. The clutch will save you from doing shear bolts which are a pain to change out with the "unsafe" shroud. Even then, engage in idle, then bring the RPMs up.
Consider a Quick Hitch. Makes snagging the scraper, cutter, etc. easier. You do have to remove it to use the post hole digger. When I had one, I made a resting cradle out of 1 1/2 pallets. Big difference in having to store and wrestle it on. Resting height has you backing up to it and the boom pins in the top link location and the bottom pins right into the links.
If you have a loader, then forks will be used more than the bucket. Moving stuff around on pallets within weight limits is the way to go. Hauling wooden posts and fence fabric out? Yup. Fork frame will be where you attach the come along to tension the field fencing. BTW, if you have sandy soil and/or gravel road, keep a pile of 3/4B minus gravel on hand. Drop a line of posts in and come with a bucket of gravel to scoop/tamp. It sets up much more firmly than sand going back in the hole. I presume you'll have beet juice in your rear tires.
Re: Box Scraper. If for gravel roads, consider a grader/scraper. That way you aren't having to redistribute what the box collects. Also, box scrapers don't do a good job knocking down pothole walls, where a scraper/grader does, especially one with scrags (ripping teeth that lower). That said, don't go too wide on a scraper/grader. They need more HP to work well.
I moved up from a JD 1025R with backhoe and loader. PTO driven post hole diggers were getting hard on me as well (back problems). Freezing in -10 while blowing snow wasn't fun either on the aging body. So while the B26 will give you great service, don't consider that the ultimate endpoint. Things like cab, third function, grapple, quick mount hydraulic auger, etc. will creep into your dreams at some point. Tractors are a journey and addicting. Welcome to the family.