That looks pretty good! Down here in New Orleans, there is no shortage of gumbo and gumbo recipes...you could literally go nuts here...we even have seasonal gumbo festivals where people make their best gumbo and it's judged...if you like that kind of food, you should really try to visit here one day.
Never heard of the lemon, but I wouldn't be opposed to it, I love lemon, so I would be curious to try it.
Yes, people use the trinity in just about all gumbo here, and filé is commonly added, but only at the very end...not cooked in too much.
A few ingredients you may find used here that differ from your recipe are bay leaves, garlic, thyme, and some different spices...like Tony Chachere's,(awesome stuff, probably similar to Emeril's Essence), some people even use seafood boil. Okra is used alot, but not a deal breaker by any stretch as far as i'm concerned. Chicken broth in place of some of the water adds a bit of depth too.
Only other difference here would be the use of sausage...you would find primarily andouille here, but anything fairly mild like polish sausage work fine....you can even find gator gumbo here, I know it sounds cliche, but it tastes like chicken, pretty much, lol.
I never had gumbo before moving here, now I feel sorry for people in the north who rarely have it...it's great stuff, it's cool to see you enjoying so much all the way up there in New England. You could probably make some killer seafood gumbo up there....crab, maybe even some lobster meat to add your territorial flare