Congrats! Sounds like you did a pretty good job for your first. The first is always a good place to learn what you want to change or what you can do better.
If you still have the gumbo, you can add a little stock to it to thin out it. It's not too late to simmer a smoked turkey wing or leg in it for a little while to get some more smoked flavor as was suggested earlier. Another option is to use smoked chicken if you don't have a good smoked sausage.
I always add chopped green onions just before serving and after I've removed the fat from the sausage/andouille. That may help you get some "brightness". You can also add a little hot sauce if you want more heat. That will also provide you with a little acid, but don't overdo it.
I've done the oven roux at 350 the entire way. I'll try 375 next time to speed things up. I usually have a pretty large roux.
If you add the okra, be sure and ask the okra lovers about de-sliming it first and don't add too much as it can overpower the flavor of your gumbo unless, of course, okra flavor is the main taste you want.
Also, it's best to make the gumbo a day ahead and taste it after it's cooled off especially the first few times you make it as it will allow you to adjust the seasonings better. It also tastes better the next day unless it sucks, of course.