Every cooker is different, so you'll have to experiment, but in the words of Gizmo "sneak up on it."
I would say start with about 1 1/2 to 2 lit chimneys of charcoal, spread them out and put about 4 splits on the coals, once they are burning close it up and see where your at. You may have to use more or less charcoal and splits. Then add 3 or 4 splits every 30 to 60 mins. The amounts are just a guess for me, I have not used a 250 size.
Another tip is preheat your splits by laying them on top of the FB before putting them on the coals. They will lite easier.
BBQ is just smoke and beers!
Usually more beers than smoke.
This is my favorite part of the whole hobby - maiden flights (burns).
I would suggest you let the cooker tell you what IT likes first.
Personally I would lean into it a little harder on a 250 and I'm going only by what my charts say cause I don't have one that big either.
Maybe 2 lit chimney's of charcoal plus 2 unlit chimneys poured over that to start with. Plenty of draft and stack and just let it run up and plateau.
Good temp to know.
Then add a little more fuel to the top of the fire and play with the draft/stack to find the point where it starts to drop.
Also a good setting to know.
After that you're just putzing around the pasture getting to know the steering and acting cool for the neighbors.
My uncle Raz used to say; "You gotta find out if you've built a good stout plow horse or a thoroughbred" - both are useful but you gotta treat them very differently.
Whew! I feel better now - so I'll shut up.
And on the eighth day God created barbecue …. because he DOES love us and he wants us to be happy.
Current smokers: Egor (trailered RF) and Easybake (tabletop pellet drive)
I run a 250 and here is my method, take it for what it's worth. I lay a base split kind of like a security blanket, I fire up a full chimney and spread that over the base split. Add a chimney of unlit and lay 2 splits across that. I used to toss in both chimneys fully fired but it just seemed to get me a coal base that was just too large and burning too hot right out of the gate. This way seems to let the heat build at a controlled pace even though it probably adds 15 minutes to the start up. I leave the basket pulled back and slightly hanging out the opening of the firebox with the door wide open and all vents max open. When I see the top two splits fully burning I kick the box in and ease the door almost closed. (I don't like to shock the coals with a sudden oxygen change) Let that burn another 5 minutes then close the door. Come back in 30 and check your temps, odds are you are still under 200. I usually add 2 small splits at this time and I start my feeding clock at this point which for me is ~ 45 minutes under ambient 70-90 temps. Then I come back in 15 minute intervals checking temps. I leave my vents wide open until I am at least 50F past my cooking temp, then I start cutting back on the oxygen supply. Like Gizmo said, you're really just letting the rig tell you what it needs but this is where my baseline ended up after several runs.
If it can't be smoked .... try frying it. It that don't work, it's probably best just left alone
I'd go Solo's way - from a man that DOES run a 250!
And on the eighth day God created barbecue …. because he DOES love us and he wants us to be happy.
Current smokers: Egor (trailered RF) and Easybake (tabletop pellet drive)