Grilling on an iron fire pit

This can easily work as a grill. A cover is not necessary. You simply need a grate that fits over the surface. I would go for a grate that fits over the rim, you don't want to worry about shifting and balance while cooking. Holes in the bottom for air flow would be nice, but again, not necessary. Start a fire, burn down to coals. You can use the "hand test" to check the temperature. Grill your product. In a grilling situation, the flavor is initiated from drippings hitting the coals, it is not necessarily a smoking situation, though you will pick up some smoke depending on your fuel.

Nice find!

Consider smashing down that dome so it is flat. Then you could cook on top of it. It would be nice if you could flatten it gently so those strips stay attached. Then it will not sag down the fire when you pile it high with sausages.

Also: coals, schmoals. You sold your drill and you are going to spend money on coals? Get a nice pile of sticks that have fallen off trees (hardwood sticks now!) and heap them up high and light them. You can get them going with a big wad of paper. When they burn down a bit you have wood coals to cook on and the price is right. And the flavor is right too!

This is a great find, especially as we enter the colder months in the northern hemisphere. I think your greatest challenge is going to be airflow: without holes in the bottom or a lid on top, the air going into your fire will all be coming from above - which will limit both the heat coming up to food you would want to grill, and also the air going into the bottom of the wood / coals.

If you want to cook food with direct heat from the fire, I think your best bet would be to put the fire on top of the bottom grate in the photo, to give it at least a bit of room to breathe underneath. This means you would definitely want a larger grate to sit above the fire.

A lid would be nice for controlling the heat, and I almost always use one for a few reasons: first, it evens out the heat and speeds things up when I'm making burgers, steaks, veg, or pretty much anything other than really delicate seafood or kebabs that call for a slower, one-side-at-a-time heat. Also, a lid helps retain heat, and ultimately saves fuel. That said, ultimately it's optional - and especially so if you're planning to enjoy the fire's warmth while you cook.

Not having vents will make ash cleanup a challenge, and again limit the control you have over the fire -- but one option you may want to consider is grilling things in foil pouches. When I was a kid, our house was heated exclusively by a wood stove, and my folks would often make something like this but with ground beef (they called it hobo stew) - and once in a while I'll break out a salmon en papillote that I picked up in the restaurant where I worked in college.

Re: other equipment, I would recommend some heavy, heavy gloves and/or long tongs if you're going to be placing things directly on the fuel. Likewise, if you happen to have a cast iron skillet or something else that you don't mind abusing a bit, I say break it out, fire it up, and see how things go with a simple, familiar dish like eggs, burgers, or grilled cheese. Best of luck!