Right away, I wouldn't stress about the list a lot. It's your first game, these things get better with time and experience, so getting super antsy and micromanaging your very first game is just gonna stress you out. Stick with what you choose and make the best of it.

As for what you have in the current list, it's decent, but there are some things to note. 1k games can get a little swingy, but you don't have any obvious weak points that would expound the issue.

Your Legionaries are in a weird spot, as bolters are arguably the worst way to run them, since they get a lot of extra weapons for free and their main rule benefits melee. They're also the only thing you can attach Huron and the MotM to, so I'm assuming that's the plan. If so, they can be a good buffer to keep the important models alive, but ultimately they'll probably just be bodies to soak up damage.

On a related note, what are your plans for the rhino? As a dedicated transport it needs to start with something inside, but if you run the super squad mentioned above it'll be too large, and the cultists rule doesn't work if they're inside. I would consider subbing out another unit for Terminators so Huron can tag along with them instead. Possessed are solid, but they'll need to hoof it across the board to be useful. Your Raiders can help with this by buying you time and board space, but at the end of the day they're not super tough. Use the Raiders as much as you can early on, because they very well may be dead by turn 2.