Look at renting a post hole digger but check to see if it'll fit the BX first. Buy one and it'll be like a plow: use once and sit around.
For your garden, you could, again, possibly rent a rototiller either to go on the BX or an engine-driven one. It's something you really don't need to use every year either. In 20 years in NJ, I rented one once. Here, if I hadn't bought a Gravely with rotary plow I would have rented one maybe a couple of times, once for my garden plot initially and once for my tree/vineyard area to initially plowup.
A longer term implement for you garden could be a what's called a Keulavator sold by Agri Supply that'll fit on the 3 ph and pull 2 disc hillers behind the wheels to make raised rows for your garden. Then buy what's called a cultivator to scarf up the rows each year before runnning the disc hillers down between them again. I've a combo device with both disc hillers AND cultivators that I have on my JD 4010 to do my garden rows every year, but that rig can't be bought now.
You COULD use a rototiller every year on your garden, but it won't do raised rows and it'll keep bringing up weed seeds.
Another option is a potato plow to do raised rows. You can get them to mount on a 3 ph. With these though, your wheels will be running down your rows and compacting the soil. With disc hillers, you can run them behind the wheels with the row underneath the tractor. Only problem you might have with a BX is it may not be high enough to clear raised rows. On my Gravely, I used the rotary plow between the rows, and the Gravely didn't have to straddle the rows. It wouldn't have done it. My JD 4010 has plenty of clearance for this.
For your road, you'll probably want a back blade to help maintain it. This is what my neighbor did for his gravel road. He uses one on his JD 4310. You COULD use the bucket for this, but you'll likely quickly wear down the bucket tip running it a lot over gravel. Back blades have a very hard, replaceable tip.
You DEFINITELY want an FEL. Can't beat having a diesel wheelbarrow for all sorts of things.
If you have any trees, shrubs or other woody stuff on your 5 acres that'll need shredding/chipping, you might want to get a good
chipper/shredder. You can buy either a DR one, Salsco or MacKissic for around $1,500-1,700 and light enough to go on your BX to do this.
If you need a lot of hauling capacity, a KK carryall with a pallet bolted to the bottom and sides built on it out of wood can more than double what you can carry in your FEL and will balance out the load front/rear really well.
Your MMM should be fine for your mowing, even in a little bit of rough stuff, but don't go chopping up brush with it.
Ralph