utility cycling

I've been riding the same Gary Fisher Hoo Koo E Koo Mountain Bike since my uncle found it in a sandpit and gave it to me to ride while away on my first internship. It was in somewhat rough shape back then, and it's kind of the bicycle of Thesius at this point as parts failed and I found ways to replace them.

I was replacing the front tire and realized I'd like to make this thing into a cargo bike (I currently use it to scout for furniture to restore on trash days, but usually have to ride home and return on foot to grab anything I find, plus I could get groceries). I'm not sure what level of standardization this bike follows and I have no familiarity with cargo bike parts, but I was thinking I'd like to add a Rear Pannier Carrier Cargo Rack and perhaps a large basket on top of that - in fact, I happen to have this homemade welded steel basket I pulled out of a dumpster a couple years ago:

It's 23" long, 12" tall, and 16" wide. I could weld on whatever mounting hardware it needs.

So basically I'm looking for advice on layout and things to add, specific parts if you have any recommendations, is that basket a horrible idea, etc. What traits make for a useful cargo bike, what would work well with this old mountain bike? And thank you for any ideas!!