Hi there and welcome!
I can't help you with any smoker suggestions BUT I can tell you that a brisket is done when it is TENDER!
Put your meat probe in the thickest yet center most portion of the Flat portion of your brisket. A 7 pound brisket is very likely to be only the flat and not include the point muscle. Anyhow the flat is the problem child of the brisket cut.
With decent probe placement in the meat you will want to start checking for tenderness anywhere from the internal temp (IT) of 195-198F.
You do so by stabbing the brisket all over with a toothpic and when it goes in all over with no resistance then that indicates that the brisket is now Tender and ready to come off. If it is not tender wait another 1-2 degrees and try the tenderness test again until it is tender.
This is probably the main practice that will make or break a brisket.
Now since you likely have just a Flat and not a whole packer brisket I would recommend you wrap that guy with double foil and a little liquid later in the smoke (like at 165-170F IT). The other approach which will be fool proof is to use SmokinAl's method and your brisket will come out with no issues. See his approach here:
https://www.smokingmeatforums.com/threads/brisket-flat-my-way.277499/
FINALLY, at a steady smoker temp of 275F you can expect the brisket to go about an hour or more a pound. So your 7 pound brisket at a STEADY 275F may take 8 hours BUT it is done when it is Tender. With this being your first smoke ever AND it being the king of all smoked meats AND with brisket being a much tougher smoke than most, I would suggest you do this the day before or plan to be finished 6 hours before you want to eat. Brisket shows NO downsides to being cooked the day before and then warmed back up in an oven. Hell it's usually better because the smoke and flavors develop even more over that time!
If you finish 6 hours before needing to serve then double wrap your brisket in foil, wrap in 3 bath towels and set on the counter or set it in a cooler. The Brisket will be steaming hot 6 hours later when you slice and serve... yes this seems like a scary idea for a beginner but after you do it once you see that it simply just works. I remember being apprehensive but committed to finishing 4 hours before serving time and wrapped with double foil and 3 towels and set it on the counter and I was AMAZED 4 hours later when it was still too hot to grab by hand and steaming hot and juicy!
Anyhow I hope this info helps and good luck getting info on how best to run your grill/smoker with a snake or other setup :)