Yes, a ballast box is just another name for a weight box. It’s an essential tool if you want to get full capacity (and safety) with your FEL. You can usually get it much heavier than using an implement for counter-balance and it’s more compact, too. Be sure you’re always wearing your seat belt (it keeps you in the seat so the ROPS can protect you if you tip over) and never lift a heavy load more than is absolutely necessary for ground clearance, etc., while you are moving. It’s really easy to get your center of balance way to high if you’re moving heavy materials around in the FEL.
What implements will be useful to you may vary from other folks, but the one that hangs off the back that I use the most is a 5’ rake. I use it to maintain our stone driveway, etc… I prefer it over a box blade for this as I do it frequently enough to only really need “top dressing”. I bought mine at Tractor Supply (in Kubota orange) for a very reasonable price. I also have a back blade that I bought used and 100% covered in rust. I reconditioned it to look like new. I don’t use it much, but it’s been handy for some things. A carry-all (a metal frame you cover with 2x PT lumber is also handy in lieu of a trailer for moving “bags of things”, firewood, etc. around, and they are cheap.
Don’t feel you have to “baby” the machine, either. These quality sub-compacts are real machines and designed for work. While they can’t do what much larger tractors can do (or can only do it much slower), it’s surprising what you can accomplish with them. Mine has paid for itself several times over since I bought it in 2002. (The BX22 is my second…I had the non-backhoe BX equivalent first, but traded it in for the more capable TLB version after a year and a half)